Apple may well soon have a shadow build of OS X running on a computer based on the new chip, assuming it looks to live up to hype. They don't have to start selling them in order to be prepared to start selling them, and even if they do at some pont start selling them, they don't have to cease making Intel-based Macs and releasing Intel-based & PowerPC-based OS X.
Meanwhile, though, Apple's already done their turn at going with a promising new chip only to have economies-of-scale allow Intel to out-develop and get ahead on the performance curve. The PowerPC really is a better chip architecture than x86, but the resources weren't there.