XS Games' PopStar Guitar (Wii, PS2) almost didn't make it to store shelves because retailers "weren't willing to stock yet another large plastic instrument."

In fact, one Wal-Mart executive "spent ten minutes explaining the problem of every single publisher coming out with a new, big controller" during a demo for the music-rhythm game.

An MTV Multiplayer story on PopStar Guitar is exemplary of the increasing use of proprietary controllers, all of which take up valuable shelf space at game retailers. XS Games in particular was forced to come up with a Wii Remote wrap-around controller instead of a full-blown plastic guitar just to get retail space for its game.

Music-rhythm games aren't alone in their shelf space land grabs. Wii Fit packs the gigantic Balance Board peripheral while the next Tony Hawk game might pack a skateboard of its own.

The PlayStation 2 version of PopStar Guitar, on the other hand, is compatible with any guitar that works with Rock Band or Guitar Hero.