It's easy to blame Manu because those two plays stick out, but isn't the horrible first half more to blame? Manu was the one who led the charge to get it close and FINALLY go up in the fourth quarter. Yes, he made a bad decision to try a play on Nowitzki, but if the Spurs had been playing well and with fire for the entire game, they might not have been in that situation. You have to know that Manu will take risks when he thinks he can change a game--such risks can go good or bad, but they are ultimately why we love him.
It just seems like Manu was pressing himself too hard during these playoffs. I wonder if it was because he was injured so often and felt he hadn't helped the Spurs enough in the regular season or because he felt that he had to be 2005 Playoff Manu again (even though that was a nearly impossible goal) or a mix of both. As has been noted by so many, Manu is hyper-competitive, but hopefully something good can come out of this disappointment and he'll learn not to press, but to trust himself.
PS: Manu, grow your hair long again for next season.