Would NO ONE open a file browser, and navigate to that media, and select that file he was interested in? NO ONE AT ALL?
Saying "NO ONE" in capitals so often doesn't really matter, because you're presenting a false dichotomy. It does matter if you go from 90% of people able to install something to only 25% of people. These numbers are totally made up, but I bet they're not totally off-base.
Now, you're right to say that there are other solutions to just making a walled garden. Ubuntu uses another method: installing from CDs is something that's pretty much never done, it has a software centre, so it has little need for autorun. But simply turning off the autorun option across the board is blind and foolish. You need to replace it with something so that the millions of Windows users without a clue can still get things done. Otherwise all they have is a large paperweight.