Impulse has always sold some games that required Steam, they were just few and far between.
Speaking of Impulse... Oh. My. God. Game Stop has taken what was once the shining beacon of digital distribution and crapped messily all over it. I've pretty much switched to Steam since they took over - which is saying a lot, coming from me. Sorry Star Dock, your baby did NOT go to a good home; Game Stop is the metaphoric pedophile to Impulse.
In fact, they don't even call it Impulse any more, and the damned thing has pop-up advertisements. It's terrible. Call CPS.