It's kind of amusing to see... I'm pretty sure people at Apple realise that just by breaking compatibility they won't force any special amount of Pre owners to suddenly buy an Apple product which does work with iTunes. They just bought Pre - why would they even look at iTouch / iPhone? Maybe iPod, but probably not before the next salary.
Also, I guess someone told them that this move has the same problem as DRM. Now Pre will improve compatibility. The only real way to block Pre would be to introduce a public key infrastructure support + certificate checking in iPods & iTunes, which I believe they don't support yet. (and it would require a mass firmware upgrade)
But they could just count on Pre users getting interested in iTunes and their store (which would give them profits). They could even detect a connected Pre and splash-screen advertise iPods to them. So... was it really something they had to do? Did they actually think before the default defensive move?