Has the exact code for a specific device ever been open?
The way I understand it there is 'vanilla' Android which is open and then there are all the devices which, even when they stay 'vanilla', still get tweaks or at very least drivers added and are not 'open'.
It sounds to me like this is just business as usual, the difference being that Google did a device specific release first for the Xoom and only now are producing the 'vanilla' branch.
I'm guessing that this isn't at all about competition from Apple or RIM. I'm guessing that Google is taking extra time to go over all of the source code to make sure when they release it they aren't inadvertently helping out Oracle's current lawsuit against them regarding Java.
There were other android releases where the opensource commit was delayed for similar reasons, in this case its to port parts of Honeycomb back to the phone branch and once that is complete than honeycomb will be committed to kernel.org.
Also note the opensource committers that work at OEMs do in fact have access..something author glossed over..as they commit code under the Apache License