Then you better not support Microsoft either, since even they have started to stop dealing with making everything backward compatible.
You might as well complain about Steam because they are internet based. Maybe, in 10 or 20 years, we'll be using some completely new technology to connect our computers into a hive mind that exists solely to subjugate all of Canada for various reasons.
Seriously. Microsoft themselves have stopped supporting Win2k. Most games that are released these days don't necessarily support Win2k. Why should Valve deal with the potential headaches?
Hell, Stardock had to release a hotfix for Elemental that actually BROKE compatibility. Why? Because their trouble ticket system was flooded with people who were using game saves from the early betas.
Backwards compatibility is a bitch, plain and simple. To get angry that people don't go out of their way for it is just foolish.

According to this thread it should still work: http://win2kgaming.site90.com/phpBB2/viewtopic.php?f=4&t=577
Valve have broken Windows 2000 support in the past before the deadline (and fixed it) but now since they have dropped support there is no guarantee that they will bother fixing it if they break it again.
I recommend using Universal Content Launcher with Steam in conjunction with cracking as many of your games as you can to prepare for when Steam no longer works on Windows 2000 if you are worried about it.
Also if you aren't already doing so buy DRM-Free games or games that are easily cracked in the future that way you don't have to worry about this stuff.
Don't bother bitching about it on forums because no one will care and all you will hear is bitching about how you should do this or that and how you are wrong for wanting to play "your" games on your computer (even though when you bought them everything was fully supported)....and somehow this is your fault (actually it is because you bought them on Steam ;) ). Just do what I said above and you'll be able to play YOUR games whever you want and however you want. Screw the naysayers.

/\ This. When you are buying a game, you should REALLY consider all possiblities: And since win 2000 is supported by ... well pretty much no-one, it makes sence Valve will say 'screw it' as well. It was hardly unexpected.

Why should Valve spend money on supporting a dead OS?

Day? Decade more like.
I can understand concerns that games on Steam won't be updated for modern OS. But as far as I'm concerned, if you've bought a game then it's yours. If the solutions that Steam or the publisher would recommend don't work then try the solution they wouldn't.

No, there really isn't.
To have "function" implies support. Plain and simple. People get angry at Steam when a game they buy from a third party doesn't work. People get angry at Steam when they get flamed by someone on the forums (but they also get mad when a flame they make is moderated). They no longer support Win2k, and people are getting angry at them for that.
As has been mentioned, Steam had broken and fixed Win2k support multiple times in the past. They just have decided to not bother fixing the support. I am sorry if that means your 10 year old OS no longer works.
So, to get Win2k working again, they would have to go out of their way to re-enable compatibility/"function", which is official support.

I'd disagree on that, function implies a bit of software can still do the task as long as the system meets the requirements. To me, lack of support would imply that you can try and use it but i it doesn't work you have to sort it out for yourself.
For example Rainbow Six 3: Raven Shield still works if you can install it on a system that meets the requirements and doesn't have something the game conflicts with but if it doesnt work, it'll do no good to ask ubisoft about it (given their consumer hostile attitude, I'd guess it's probably not much good asking them about modern games much less old ones)

No, sorry.
They are blocking any function of Steam on Win2000... that is not the same as a game company no longer supporting a game on Win7 but letting you get it working if you want to, which is usually extremely easy. It's completely different.
And again, I am not saying Steam is wrong here, I am saying only that the end of it functioning on an old OS is something people should consider before buying on Steam rather than keeping the game independent of such a program.

Ah... Logic Audio...
Try to save some money for FL Studio. One purchase will guarantee you a lifetime of free updates (to minor and major versions). ;)

It also occurs to me that this might be the start of a move towards a 64bit version of steam which has to eventually come since win7 is supposed to be the last MSOS that'll support 32bit

I'm frankly shocked I still need to put "-32bit" in my Half-Life 2 command line every time I install it to avoid getting a buggy piece of crap version of the game.

It's funny how these threads always ends up attracting a bunch of people who just has to comment on how stupid/whatever it is to run an older OS these days, and having the nerve to want stuff that always worked before to continue working. Guys, we already know what you have to say, just shut it. Ok?
(of course, the most amusing situation was when I used XP and everyone else apparently jumped to Vista. XP was soo outdated, of course I couldn't expect stuff to work on it. I had better "upgrade" to Vista - which I had used and knew was a piece of shit OS - as soon as possible. Well, guess what, I didn't. Now Vista is obsolete as well, and I saved myself the money and the bother).

The bigger question here is why the heck don't you image the drive and throw it in a VM? Seriously now, keeping a machine running a decade old OS for just one piece of software that can easily work well in a VM (and no, you won't have any latency issues) is just silly.

Nah its just been patched and renamed Windows 7