I suggested software update because "Apple Software Update" (the Windows program) is required to be installed on Windows Boot Camp partitions, while iTunes is not. Apple likes all-encompassing, "we'll take care of everything" experiences; they wouldn't just go through all the trouble of making it work on the Mac side and then leave off Windows support (thus making the Apple Software Store the first thing you'd install on any Windows computer, in order to pull down all your favorite applications—convenient for them, isn't it?) It would be much harder to convince people to install iTunes in order to install, say, Photoshop, than it would be to convince them to install a single-purpose general-software utility.