Well he goes through his progressions quicker and makes better decsions, plus his release is much quicker. Actually the only think Simms would appear to be better than Grads is his deep ball......like others have said Simms is a one trick pony. 
The question I have is given the deep ball is not Grads strength, and it isn't right now, why is he throwing so darn many of them? Entering the NYG game he was 2-20 or something liek that. He threw at least 4 more my my count so in 4 games he's averaging 6 deep balls a game? Are you kidding me? The odd thing is Simms clearly wasn't going that vertical in his games so it is like both guys are trying to show they aren't just what the scouts think they are or something.
Well the thing is the Giants were daring him to throw deep. On a few occasions Grads showed he could do it even in those conditions and the Giants started to back off a bit. This is why I was dissapointed in that Gruden did not try to run the ball more in the third quarter. The Bucs showing they could move the ball through the air opened up oppurtunties for Carnell to run. The Bucs offense was extremely conservative in the first quarter and the Giants were shutting them down. The second quarter rolls around and the Bucs start going pass happy with an empty backfield. But it was working the Bucs were moving the ball through the air and the Giants were caugh a bit off guard by it.
The only time where Bruce made a bad decision with a ball deep was when he was trying to force it in with three Giant defenders nearby. Other than that he took what the Giants were giving him.