Because the music store is only compatible with the iPod, a customer who wants to abandon Apple's player in favour of something else must replace all the music he downloaded from the store. It is as though a person's entire record collection worked on only one brand of gramophone. Hence with each song a customer buys, he binds himself a little more tightly to the iPod. Apple offers its customers a 'Trojan horse', according to Mr Shope. Customers embrace its iconic device, and then, like the hapless Trojans, find they have fallen into the hands of the gift-givers.
This thesis is only supportable if you ignore the original feature of iTunes, it's ability to burn CDs. Long before the iTunes Music Store, Apple ran the Rip, Mix Burn ad campaign, saying 'it's your music - burn it on a Mac'. When they introduced the iTMS, they retained this feature, so you can burn Red Book, uncompressed, unencrypted CDs of your iTunes Store purchases.
This is in fact the only reason I buy music from iTMS - if you do, make sure you burn the CDs as backups. And don't buy the videos - you can't burn them to DVD.