Here's the rule from the NFL Rule Book on Completing a Pass:
http://static.nfl.com/static/conten...pdfs/11_Rule8_ForwardPass_BackPass_Fumble.pdf
COMPLETED OR INTERCEPTED PASS
Article 3 Completed or Intercepted Pass.
A player who makes a catch may advance the ball. A forward pass is complete (by the offense) or intercepted (by the defense) if a player, who is inbounds:
(a) secures control of the ball in his hands or arms prior to the ball touching the ground; and
(b) touches the ground inbounds with both feet or with any part of his body other than his hands; and
(c) maintains control of the ball long enough, after (a) and (b) have been fulfilled, to enable him to perform any act common to the game (i.e., maintaining
control long enough to pitch it, pass it, advance with it, or avoid or ward off an opponent, etc.).
Note 1: It is not necessary that he commit such an act, provided that he maintains control of the ball long enough to do so.
Note 2: If a player has control of the ball, a slight movement of the ball will not be considered a loss of possession. He must lose
control of the ball in order to rule that there has been a loss of possession. If the player loses the ball while simultaneously touching both feet or any part of his body other than his
hands to the ground, or if there is any doubt that the acts were simultaneous, it is not a catch.
Item 1: Player Going to the Ground.
If a player goes to the ground in the act of catching a pass (with or without contact by an opponent), he must maintain control of the ball throughout the process of contacting
the ground, whether in the field of play or the end zone.
If he loses control of the ball, and the ball touches the ground before he regains control, the pass is incomplete. If he regains control prior to the ball touching the ground, the pass is complete.
To me, the underlined portion is significant here. When Bryant went to the ground, he had control of the ball. At the time he hit the ground, he had control of the ball. It was after he hit the ground that he lost control of it. In losing it, it never contacted the ground without him being in possession of it: it came loose, and he secured it before it hit the ground. On that basis, reading the rule as written, the play was a catch, and should have been a touchdown.