I think it's pretty unrealistic to say that rondo didn't go for the score because he feared a chasedown block. This is the same player who attempted to dunk ON a defender that same game without showing fear of a block. Additionally...most defenders wouldn't even attempt to block a player that far in front of them, because it's not worth risking them getting the hoop and free throw after for the contact.
I've never seen rondo take anything off his attacks out of fear of the defense. I have however seen him stop fast breaks, and force passes on mismatched situations, in the pursuit of assists all season.
He had another play in todays game where he was leading a 2 on 1 break, and instead of finishing easily himself, he passed off to ray or baby who was trailing, leaving them with a more difficult (and contested) layup to convert. Fortunately we came out of that possession with a score.
As for the pierce play at the end...you can see that he's already in the motion of spinning towards the baseline once his defender was off balance by the up fake. He didn't think the defender would be THAT off balance, or I'm sure he would've drawn the shooting foul. You can see his mind was already there, because he still threw the ball up after. Fact is, Rondo blew the play trying to pad his stats.