Well, first the ones complaining are of _course_ not all of the ones who actually have a problem. Many might a) not know that iTunes is at fault or b) just don't complain on the 'net.
And then: You don't really think that per song there's one buyer on a Windows machine, right?
I'm not saying it's a biiiiiiiig problem, but you certainly don't want to pay for songs you can't download for one thing, and you certainly don't want iTunes to kill other things like the _reading_ of data CDs... (which sounds like iTunes on Windows overwrites some important shared libraries to me...).