Yeah, they're the end credit theme for Portal and Portal 2 respectively. And I figured copyrights would play into that kind of stuff. =P But still, would be interesting I think.

Though would be somewhat worried that it might not be as good, because they're both kind of sung with a "robotic" voice. I heard a cover of the song by the lady who sung the song for Plants vs Zombies yesterday, and while it was nice and I may totally add it to my "Music To Do Homework To" playlist, it just didn't have the same catch to it.