Found an interesting article on this very topic. This article was written around midseason of last year and tracks all passes to that point from the 3-7 yard lines.
* Of throws that went to the sidelines in the end zone (mostly fades I'd say), 24.5% were completed. That's a pretty small number, and it illustrates just how difficult it is to throw and catch that type of pass. Ben's game-winner to Santonio is amazing because of the degree of difficulty of the throw and catch. The ball has to be lofted perfectly over the outstretched arms of an NFL DB, who will typically have about a 37" vertical. It has to travel at a trajectory that, once it gets past the DB, will wind up catchable WHILE the receiver stays in bounds. It's not simply a matter of "throw it high and the taller guy will catch it." If that were the case, there wouldn't be guys like Brandon Marshall who are great receivers and stand 6'4" but can't catch a short pass in the end zone to save their lives. And there wouldn't be turds like Sweed and James Hardy who are 6'5" but can't make a roster. I mean, if height is all you need, then how would any wideout who's 6'3" or taller ever go unemployed?
* In fact, taking the whole sideline thing out of the equation, we see that only 33.8% of all passes into the end zone were completed. The ****'s hard to do. On the other hands, 66.7% of all passes thrown short of the end zone were completed. This is how guys like Wes Welker and Victor Cruz get schemed into the end zone. Neither are big and neither are particularly physical; they create absolutely no size mismatches whatsoever on a secondary. Yet they tend to catch 8+ short TDs a year, because their offenses use their shiftiness and toughness. Not their height.
In other words, most of the time, your red zone success comes from throwing short and working into the end zone. Not throwing it up for a 6'5 guy to leap and catch it.