Somehow it makes sense to me not to release Honeycomb into the wild.
Google tells us it is about the scenario where Android 2.3 and 3.0 have to live together.
The Chinese will produce bad 3.0 phones, while manufacturers that go for UX will stick to 2.3.
Consumers will go for the higher version number. They've learned that is most important, especially a major version.
And they are disappointed, and may decide Android is bad.
That said, Google could solve this by releasing a "3.0 for phones" (which is just 2.3 rebranded).
So... is it to reward hardware manufacturers that dropped a lot of code? I wouldn't be surprised, given that the Honeycomb is a fork. Mfg X may well have suggested to Google: we built this together from your open source project, and you can have it (saves us on maintenance and gives us market acceptance) - but we'd like to keep it to ourselves for now.
Or Google thinks that keeping Market access and the Google apps is an insufficient differentiator, in which case we can look forward to a close sourced future. But then fragmentation would start - and it is already starting with the Android compatibility on BlackBerry tablets.