The only replay where one could suggest it shows the ball hitting the dirt is the extreme closeup on the catcher's glove, and even that is inconclusive.
The part that bothers me about that play isnt that the ump got the call wrong, it happens, but that he failed to communicate the call. He signaled strike three, and he said nothing about there being no catch. I can understand Paul's reaction. Lacking an indication from the umpire that the ball was still live, his reaction was normal.
For anyone who wants to see several replays, go to
mlb.com and click on the video link "Pierzynski's K in ninth" right below the banner for the main article.