iTunes and the iTunes store are fantastically successful. Proactively crippling the ability of a 3rd party to sync with iTunes (an ability which was developed without cost to Apple) to protect the iPhone is a dangerous cross-market precedent. If Microsoft tweaked Windows so that Boot Camp didn't work, the Apple community would be livid...but Microsoft doesn't sell computers, so why do they care? I'm no fan of Microsoft, believe me, but I'm not going to be a blind fan of Apple in all that they do, either. They're a company, and they sometimes do Bad Things in the name of profit. That being a company at all makes this their nature is of no consequence, we should be advocates for users wherever we find them.
3rd parties can sync with iTunes libraries. The law doesn't care about what is convenient and what isn't. For the matter of dangerous cross-market precedents...
Proactively crippling the ability of a 3rd party to install Mac OS X to protect the Mac is a dangerous cross-market precedent.
Proactively crippling the ability of a 3rd party to install iPhone OS to protect the iPhone is a dangerous cross-market precedent.
Proactively crippling the ability of a 3rd party to install Sony Bravia firmware to protect the Bravia LCD HDTVs is a dangerous cross-market precedent.
Proactively crippling the ability of a 3rd party to install WebOS to protect the Palm Pre is a dangerous cross-market precedent. (you can't install it on anything else, now can you?)
You also still have yet to prove that what Apple is doing is 1) not in the spirit of competition (forcing the competition to come up with their own, possibly unique ideas) 2) illegal and 3) that convenience factors are a matter of law.
iTunes doesn't cripple access to iTunes Store content for other players. And by this I mean impede -- copy files or using an XML sync program is easy enough. End of story.