eh, it's hardly a dime but the underthrow isn't necessarily unintentional either.

when a receiver has a defender beat the defender has to enter catch-up mode and simply run as fast as he possibly can with his back turned to the ball. this makes the defender susceptible to short throw, which they can't possibly be aware of (since their head is turned as they run at full speed) and can't stop for. now normally you'd say "why not just throw it ahead of the receiver who has the defender beaten anyway," but with the end zone there wasn't a lot of room ahead of Moss.

Brady does this quite a bit, and it works enough that you eventually stop wondering if every one is an underthrow. he also does it a lot on the sidelines on 10-20 yard throws where an underthrow doesn't make nearly as much sense as the throw being intended that way.