I have games on Steam. In order to play them, I need to have Steam installed on my computer. If I uninstall Steam, I cannot play those games. That's what I'm talking about. For Impulse or D2D or most other DD services, that isn't true. You don't need to have a 3rd party program installed to run the game, the program you need is for downloading and installing the games, not running them. If I download all my Impulse games right now and then uninstall Impulse, I can still play those games. That's the difference I was trying to emphasize.
Maybe I shouldn't have said Steamworks. I don't know if that is the same thing as I am describing above. Sorry for the confusion.
Yeah, Steamworks is different. All Steam games require Steam in some form, but if you buy the game somewhere else you don't have to use Steam. Say, Oblivion retail does not require Steam, nor does the Impulse version. (The Steam version does, of course.)
Steamworks changes that. If a game is Steamworks enabled, *all* versions of it require Steam because Steamworks requires Steam. Fallout: New Vegas is a Steamworks game and any version of it you buy requires Steam. If you buy it at retail, it installs Steam. Magicka on Impulse is another example, it requires Steam.
So if for the purpose of discussion we ignore the contractual issues, they could put Elemental on Steam today and it wouldn't affect anybody who bought it from Impulse. All it'd do is allow people who prefer Steam the ability to buy it from their service of choice. If they made it use Steamworks on the other hand, everybody who has it now (including Impulse users) would need Steam to play it.