It is acceptable and legal to resell software (at least in Canada.) The Copyright Act of Canada states that a person can have up to four copies of any given software title (for personal use) which he or she owns a license. That is; the original, a backup, a "format shifted" copy (to stay compatible with changing systems, for example) and a backup of the "format shifted" copy. It then says that you must delete or destroy all copies if you sell or gift the software.
My point is that copyright is very tangible and no EULA/contract is valid if the terms are illegal. A developer can tell you not to make copies or resell their product but you have every right (at least in Canada) to disregard their ignorant demands.

Yeah but these people are the sort to whom money is an all or nothing concept, the amounts are pretty irrelevant and they're as likely to sue you for costing them 20 cents as they are for a million bucks.
I do agree that the disposable nature of it lowers the chances of them bitching too badly but if the game indusry ends up pressuring resellers into paying them off, the movie & music companies won't be far behind. I reckon they're watching this battle keenly to see if they have a chance without actually wasting their own resources on trying.

And I suspect it is the same here in the UK because there are shops doing so here.
But then I would argue that you need to ensure you are well-informed before you part with your money as well as fight for your rights as necessary.
I once made the mistake of buying a DRM-protected music CD that refused to play on my PC or my car CD player. I went straight back to the HMV store where I bought it and demanded my money back - they refused, so I demanded to speak to the manager.
When I forced him into a corner about it being "acceptable usage" to be able to play the CD in my car and on my PC, he had to refund my money.
The point is that it's important to keep well informed and know your rights - as well as not parting with your money too easily! :-)

QFT
Good for you for exercising your rights.

This discussion is about the second-hand market, which is entirely comprised of physical goods, so my comparison was indeed like for like. Digitally distributed materials are not sold second-hand so are a side issue.
Additionally, when you buy a physical game you do indeed own that copy of the game, and your ownership of that copy entitles you to certain legal rights as a consumer and owner the same as with any other physical object you possess. "Click-through" license agreements are not considered legally binding (for a variety of reasons) and are not allowed to overrule the "first sale" law in the U.S. or the comparable laws in several other countries; briefly, "first sale" ensures that the seller can only impose restrictions and limitations on the first buyer; these restrictions cannot be passed on to anyone they transfer the product to nor can their terms prevent its transfer from occurring; the second-hand buyer gets the item with "no strings attached" other than those added by the person they directly bought it from (if any).
"First sale" applies to absolutely any physical object regardless of its form or medium, so my comparison of a car to a retail video game was entirely accurate. Digitally-distributed material is intangible and is typically sold as a "service" (not a "product"), therefore it is not subject to the "first sale" law.

Additionally, when you buy a physical game you do indeed own that copy of the game
No you don't. And that's the problem I guess. People assume they own it as they have something physical to hold, but all you've actually bought is a license to use the data contained on the shiny media you bought. You basically own the box (but not the design or text printed on it), you own the material the manual was printed on (but not the content) and you own the DVD the game is distributed on, but not the game.
Same with movies, music CDs and books. While the publishers of those items may accept the second hand market, it appears that software publishers do not. Good luck trying to change their minds though.

It's sad how business is moving from ownership to license, where you are entitled to use the product as long as the publisher wants you to. Games have activations that may or may not work 5 years from now (or like Gears of War which stopped working earlier this year by "accident"). Music industry tried to add different solutions of copy protections and mostly they just caused problems and bad blood.
Digital games industry usually try to act as "good guys" but most of them can solely say when something works and when not. Amazon can delete e-books from users if they feel like it... Steam can cancel accounts if they feel like it and you may not get any support on your cause as you probably are already tagged as an evildoer without having a right to defend yourself and your property.
I am a Steam user and will stay so because of some games that are only playable through the service. Still, I'm a consumer and mostly because I live in Europe, I have to stay on my toes and compare prices. Sometimes retail wins, sometimes digital. Heck, I have to even see if I can get some "real life" items like guitar stuff cheaper abroad. I've seen even 100 euros price differences without that special reasons (not in local stock and the item goes to distributor for repairs anyway if something goes fubar...).
I am a consumer and it's my right to choose what I buy and what I do with the product I've bought. Of course publishers would love to sell the same item for me many times and in many formats.

You own the physical product and a permanent* licence to use it but not the content itself.
*Exceptions made for games irrevocably tied to Steam. Hmm thats a thought, is making a 3rd party application a system requirement basially bypassing fair trade because it removes the option to NOT use steam?

Perfectly fair but I'm thinking of Dawn Of War 2 & Empire Total War, non valve that require steam

If I was to play devil's advocate here, then Valve/Steam could just turn round to you and say "It's our game, we can distribute it how we want to and if you don't like it then don't buy it."
That would work for their games, sure. But not the vast majority of games they sell =)
To me it's black and white - give me the option of "free with adverts" or "paid for with no adverts".... nothing in between.
In all fairness, you can turn those "adverts" off. Then you'll never see any of them again, and if you set your default window as any thing over than the store, you'll never even see anything being sold either; unless you choose to.

Do you "need" Steam for those two? Can you not just buy them as boxed games?
To be honest (and it's another of my Steam bugbears), the prices on Steam for downloads seem little different to buying the boxed games in my experience - so if I didn't "have" to buy it on Steam then I probably wouldn't...

I will not understand,why people pay 50 or 60 euros just to "rent" (buy a license) a game on Steam.I don't even trust their "top sellers" list .

You can indeed buy them as boxed games, its how I got DoW2 (well i WON it rather than bought it but same difference), but they are 100% irrevocably tied to steam (barring cracks that I don't know about but since DoW2 is about the only PC game I play online, I need the online service)
Yes but MOST non-valve games are available elsewhere

'cause I don't have to carry shitload of CD/DVDs around with my notebook when I'm going somewhere - and I'm going somewhere a lot and I always make sure I have net acces there :D