Maybe you weren't waiting up til 4am EST, eagerly anticipating the release of Angry Birds Space. That is what you have us for, after all. If you were, though, you might remember that only one version of the app made it to the Play Store that night: the free version. Later, though, Rovio released "Angry Birds Space Premium," which is the ad-free version of the app. Now, Rovio has released Angry Birds Space HD. Sure. Why not?
This breaks Rovio's tradition of only having one version of its app on the Play Store. As you can see below, all the other versions of Angry Birds have one app on the Play Store.