It's not so much that they impose region restrictions, it's that they aren't good at negotiating a global contract. Region restrictions are almost always enforced by the publisher.

Incidentally, I did find out that they plan to fix this loophole.

Well, just made my first purchase from GamersGate. Brothers in Arms: Hell's Highway for $7.50 was too good to pass on.
Hopefully I have no issues.

Most likely it just means it's not the demo version.

Big Fish Games use a client for downloading/installing and activation. But it doesn't need to be running in order to play most games (some games, however, will launch the client on exit). You can download games as many times as you want (as long as the game is still on there server -- in the past they have removed some due to licensing issues).
The reference to "full unlimited version" simply means the full game and not the 60/30 minute timed demo that you can get for free.
Before they release a game, Big Fish do test them. They ensure that they work for the majority of customers, they ensure there are no virus alerts (and will help to resolve false positives too). There are no adverts of any kind displayed either on their site, via the client or in-game (with the exception of advertising games that they sell).
In terms of DRM, the only DRM is their client and the activation server you have to go through. There is no SecuROM, Starforce or anything "sinister".
Further to that, Big Fish's support is without a doubt some of the best in the business. And compared to that of Steam's they are on opposing ends of the scale. Any problem or query to do with Big Fish sold games or the site, will be answered fairly promptly and very politely (and chances are, they will go above and beyond your initial concern).
They've even dumped their tiered pricing so that games are now $6.99 for everyone whether you're a member or not.
The ONLY downside is that during purchase of a game you will automatically be signed up as a member unless you hit the check box to opt-out. That really should be an opt-in request as once you're a member they will bill you the cost of one game per month (as a game credit).
I did actually join their site as a member earlier in the year and haven't regretted it at all.

Does D2D have an online activated installer for their stuff? I've been using GamersGate for a few purchases due to the loophole mentioned here, allowing their installer to be bypassed, just leaving you with a regular copy of the game.
But today D2D has some good sales on, like STALKER for $10, and I'm interested in And Yet It Moves as well, which they claim is DRM-free.
This is going to be an expensive week. Colin McRae on GoG, Possibly a few games from D2D, who knows what GamersGate is gonna do for the rest of the week...

Activation with D2D is on a case by case basis and they aren't very good at making it known.
who knows what GamersGate is gonna do for the rest of the week...
Just a few one day sales now I expect. Seeing as they have a huge number of discounted games in the Paradox sale (spanning 3 pages dammit!) and the Crazy Machines pack....

Hmm, I'd really like to check out STALKER, but a requirement is that I can back-up and install my games as I feel like. Not sure I want to take that risk from D2D then...

EDIT: Wow, I just asked the same question I asked directly above this post. Fail for me.
I'll ask this instead.
Has anyone bought Trine from D2D, and can tell me if it has some kind of internet check for the install, or could I safely back it up to a DVD and actually own the game?

They say it's DRM free. So that would rule out the possibility of an online activation. If it does require online activation then that's false advertising.
Oh and I would avoid Impulse. My games have disappeared from my account there. I've sent them an email. I hope I can get that sorted out.
Steam isn't so bad, so long as you've got broadband. It doesn't have an offline mode worth mentioning.

Trine has the DRM Free logo on the info page, which I believe indicates that neither the publisher nor D2D require any online activation for it. You could probably email support and find out for sure.

I bought Cogs, AYIM, and Bride from D2D... all DRM-free and I didn't see any online activation. Just download the installer, pretty much like GOG.