My interpretation is that the OS development has been "spiked" to target certain platforms, as a proof and exploration of the tablet form factor. But, as with most fast, targeted code pushes, some sacrifices have been made in the generalizablility of the code base. They may want a chance to go back and smooth out their hacks before eager vendors get their hands on it and start building the first at large generation of tablets.

This is just one interpretation, but it's an example of a case where I'd be behind Google's actions.