While it's true that a QB's success rests partly on his supporting cast (football IS the ultimate team game, after all), it doesn't answer why Trent stares down his receivers so much, something Montana couldn't be accused of doing. You don't notice it as well from TV and I'm not sure how well you notice it from the sidelines, but he's had a habit of looking over at the WR the play is designed to go to before the snap...and he keeps watching that WR all the way through his pass route until he throws the ball. It's a wonder he hasn't thrown more interceptions than he has but the fact that he's thrown 25 picks as opposed to 24 TDs can be traced back to this problem.
Let me take you back...MNF vs Dallas
3rd and 8 from the Dallas 11 6:21 left in the game..Trent had his head pointed directly at Lee Evans before the snap and he followed him throughout his pass route all the way until Terence Newman picked off the pass.
http://www.nfl.com/gamecenter/2007100800/2...post-playbyplay
Admittedly, he doesn't do it that bad on every play but he does it often enough that it's a major issue. During the Open Practice a few weeks ago, I sat in my seat as opposed to along the sideline primarily to see if Trent was still doing it...and if he had heat vision, he would've set Roscoe Parrish on fire the way he was staring him down. If a fan can see it from the endzone, you know NFL DB's are going to keep seeing it.