What I find strange is that Apple says the iTunes store exists just to sell iPods, but surely if they opened the iPod to other music stores by supporting WMA format as well, they'd sell more?
It also would be a good way of 'switching' users of other music stores to iTunes (they buy an iPod for WMA, realise it supports AAC as well so they start using iTMS).
Perhaps Apple wants to 'lock down' the market by controlling the format the music is distributed in, but I have a hard job believing Apple will be able to maintain that kind of monopoly in the long run.