An analysis and thread responses by those with expertise in the field courtesy of Texas Booster on a previous thread:
http://www.weathergraphics.com/tim/af447/
Well worth the read.
Very much, and the comments too. Thanks!
Summary (of a comment? and extrapolated): the tail section (empennage) may have broken off due to turbulence, leading to near-instantaneous decompression, and the resulting g-forces would have kept the pilots from doing anything in the few seconds of consciousness left.