It is worth mentioning that McCoy's senior bowl arm measurements were a little shorter, at 32 5/8". So, he is probably a little shy of 33", despite what the combine website says. Not that it is much of a difference, but it could show why lack of length is consisently mentioned in scouting reports, as those are largely being finalized by time the combine comes around.
Additionally, he doesn't get beat very often at all, and when he does it is noticeably due to an opponent's length advantage. It stands to reason that while his length isn't a huge detriment, it is still one of his very few, and minor, weaknesses. People just notice it more because he rarely loses otherwise.