As long as the Pre is capable of syncing with iTunes, you have a situation where an unsupported device is capable of affecting (through fraudulent means) the user's music, contacts, settings, and god knows what else -- all of which live in Apple's operating system, inside Apple's software.
If Palm fucks anything up and some fraction of Pre users manage to corrupt their data or their software (because Pre-iTunes interoperability is an ugly hack!), then those users are not—at least not all of them—going to shrug and say, 'Oh, well. I was using unsupported software and hardware, and I got burnt.' Enough of them are going to say, 'What the fuck!? iTunes/Apple/Mail/OS X sucks!' or they're going to call Applecare support and sit on the phone for half an hour while the poor schmuck tries to get their iTunes library back. That is what we call a bad experience, and Apple doesn't like that. If they control both sides of the equation, then they can make sure that doesn't happen.
So I guess Microsoft should be able to block any other browser because Chrome might crash and someone could says "Windows Vista sucks" (which it does but that's a whole 'nother story)
Beyond that, if that scenario does happen Apple gets to tell it's customers "Look, Palm messed up your data which is why you should use geniune Apple hardware" and they win a monsterous victory. Palm corrupting iTunes data would be the greatest thing to ever happen to Apple. So the idea that Apple is blocking the Pre because of that doesn't hold much weight.
Vista requires signed drivers because Microsoft was finally sick of shoddy drivers destabilizing Windows, generating support calls and ruining the user experience.
So there's no need for the hypothetical. Microsoft has already done something analogous to Apple's move -- despite years of 'enjoying' what you view as a sales opportunity.
That's a bogus analogy. Apple is not preventing you from installing any software you want and using the same music you have in iTunes (along with all the meta-data in the music files) to connect to any hardware you want through standard USB/Firewire/Whatever connections.
Apple is preventing people from essentially hacking their software for the benefit of another company.
Have you worked in tech support ever? Nobody gives a toss why their data is gone, only that you can't get it back. Finger pointing "It's not our fault it's theirs" is terrible, even if it is true.
They don't win a Monstrous Victory. You know when Windows crashes, it now submits to a web service and comes back saying:
Your computer crashed because of software made by JONES SOFTWARE LTD.
I feel less annoyed at Microsoft when I see that, but never happy. It's still not OK. It's not a victory for MS, just a defensive block.
If Palm fucks anything up and some fraction of Pre users manage to corrupt their data or their software (because Pre-iTunes interoperability is an ugly hack!), then those users are not—at least not all of them—going to shrug and say, 'Oh, well. I was using unsupported software and hardware, and I got burnt.' Enough of them are going to say, 'What the fuck!? iTunes/Apple/Mail/OS X sucks!' or they're going to call Applecare support and sit on the phone for half an hour while the poor schmuck tries to get their iTunes library back. That is what we call a bad experience, and Apple doesn't like that. If they control both sides of the equation, then they can make sure that doesn't happen.