I heard someone waffle on buying a game on the App Store he wanted because it was two dollars instead of one. Price matters. Once again, we're not talking people who have old Guitar Hero controllers lying around or are familiar enough with them to feel good about buying cheap/used, we're talking people who watched Guitar Hero and Rock Band happen from the sidelines and thought "That does look like fun. But gosh, a whole new controller? That seems excessive."
Also, I have Audiosurf. It's OK. I find the rules it plays by often don't sit well with the maps my songs generate. (I can't get a combo going because there's just plumb a lack of blocks for a stretch.) It looks nice, I'll give it that. And since the similarities between this and Audiosurf pretty much end at the visuals, not a bad thing to nick. But hey, maybe you're right. After all, Boggle failed its first year because people just played Scrabble instead.