Moral of the story is there's no sure thing in football.
Which decision has better odds aside, you have to consider the other element:
What message does the coach send to the players?
Whiz sent the message that he trusts his team and the fact that he did it again after having fumbled in the exact same situation the previous week has to make Ryan Williams much more confident.
If you kneel there, you're telling you offense you don't trust them. It's not even that you expect the first down, it's the fact that you won't even try. If I was a player and my coach wouldn't even give me a chance to close the game out, I'd be pretty bummed to say the least.
Speaking of closing the game out how cool was it to watch Arizona actually run off almost 7 minutes of the 4th quarter on a 13 play drive that included 9 runs!