I don't see how this hurts Apple at all--in fact, it seems to me that it should *help* Apple.
Remember, the point of the iTMS is NOT for it to make a huge profit (though that would be a nice bonus); the point is to push iPod sales.
Napster songs being able to play on the iPod = even more iPod sales, I should think. Granted, Apple has probably lost out on some amount of *licensing fees* by not licensing FairPlay (and thus "forcing" Real to come up with their own way of making 'em play), but it doesn't seem like it should hurt them.
No, on the other hand, I think that Apple doing the reverse--allowing iTMS songs to play on non-iPods--would be a *bad* idea, since that would discourage iPods sales.