They still haven't open sourced Android 3.0, in which they said they would never release that part of Apache licensed code to the public.

So there could then be a possibility, again be hidden APIs so that their tablet app offerings could be better than others.

I personally think that, if you claim open source, some should be able to obtain the code if they are using the software itself. I clearly don't think a normal android tablet user would reasonably grab a copy of that source code.