I noticed this recently when I looked at the Impulse client after an update and saw the GameStop logo. I looked up some information on it and Stardock sold Impulse back in March 2011. You can read more on the story at PCWorld.
Many people were upset since GameStop does not appear to care about PC gamers in its retail stores; it either carries no PC games or very few in the back of the store on a single rack. I have not noticed any changes yet in the service since GameStop purchased it. I know GameStop was selling digital versions of PC games through its online store so maybe it wanted a better outlet to compete with larger PC game sellers such as Steam. Hopefully GameStop won’t screw up Impulse by making it some kind of hybrid PC / console game seller.