This is my first post, but I'm a long time reader and I think I can contribute some information. First of all, compare the pictures of the recovered stabilizer with this one:
http://www.eads.net/800/en/gallery/a...4/42002549.jpg
If you look closely, you will see that the stabilizer is indeed fairly intact and the part with the mounting points is also still there (though under water). So obviously it must have been that bolts that failed, the stabilizer didn't break apart. Only a small part at the rear is missing.
I guess it's plausible that the stabilizer detached when the plane hit the water. I would like to point out though that the radio antenna is located in the vertical stabilizer, so the crew would have been unable to use the radio if the stabilizer had detached during flight, while the Satlink ACARS messages would still have worked. Not drawing any conclusions, since that's up to the investigators and, also we don't even know where they found the stabilizer, and there could be a thousand other reasins why the crew didn't use the radio, but still an interesting fact.