I really like the concept of this website. Supports indie developers and charities. Only real dislike is that most of the games you have to get from Steam. That really does not make it DRM free. That is my pet peeve, not need to derail this thread because of that.
Are you talking about the same website as the rest of us? Most of the games so far haven't had Steam keys and the ones that have come with Steam keys have had a DRM-free download directly from the IGS site as well. The one exception is the current game, which isn't really DRM-free, but it's not on Steam either.
In summary, there have been no Steam exclusive games so far and it sounds like you talking about a different site.
EDIT: There's a list of past games in this thread I made