^^Streaming content is different from installs. Even games on the original Xbox did it. For example, when you played multiplayer on Halo 2, when you loaded a map for the first time, it stored it temporarily on the hard drive to allow for faster streaming, and deleted it afterwards.
Besides, PS3 is getting lambasted for REQUIRING it--even if they did have an install feature on a 360 game, they wouldn't make it mandatory for obvious reasons.