Open Standards and Privacy are not opposites...
... if Apple opened this protocol to other makers (note, I did not say "open source it"), and allowed any maker of hardware to write a client for it, then fine; otherwise, put it back in the bin marked AppleLink. A better MMS would be cool. It doesn't have to be Apple's solution either. I'm open to anything that would have the broad reach MMS does, but work better. But it must allow me to talk to my friends, regardless of what they're using.
The problem is that, like FaceTime, this is just another closed, Apple-to-Apple technology; and we've been here before with the email wars of the 1990s. The reason RFC-822 (and successors) and POP3 won back then wasn't because it was the best; it was because you could send a mail to someone and be pretty sure it'd arrive saying more or less what you'd written. Interoperability is king in communications. This is why GSM took off, and CDMA didn't.
Interoperable and "Open" don't mean the same thing as "Public" or "Shared". There are open standards for point-to-point messaging that do not expose their information to scraping by the likes of Google: XMPP (Jabber) is one that springs to mind. Just because Google (a major provider of XMPP) records everything you send on GMail Chat, it does not follow that the protocol itself does this - Google own the relay server, that's why they're recording the info.
(Incidentally, the same thing happens to your SMS traffic; but this time it's a telecoms company, licenced by your government, that does the snooping - to me, that's better than having a corporation doing it; Americans generally think the opposite...)
BBM is not a good precedent, because a. there's not much of a financial barrier to owning a BlackBerry*, b. Large companies issued them to employees en-masse, c. iPhone owners already use open systems like Twitter for these features.
A communications service is only as good as the number of other people it can help you reach. Something that only 20% of "smartphone" users (smartphones being only 30% of the market anyway) can use isn't much of a draw...
* don't fall for the line about "FREE" contract pricing: over 70% of mobile customers in the EU are on Pay-as-you-Go plans, and €600 for a phone is beyond most customers' means or willingness to pay.