I have to just say that a player's wingspan and reach most definitely are important to whether he can be a good defender. I don't how one can say otherwise. Obviously there are other factors, but you need the physical attributes, as well. Rondo wouldn't be the defender he is if he didn't have such a long wingspan because he wouldn't be able to cause so much havoc. I'm not saying that Rondo wouldn't be a good defender if he had a shorter wingspan, but he's definitely a better defender because of it.
I'm not saying Kemba can't be a good defender, but he'll have to overcome his rather average wingspan and reach, especially since he doesn't have a lot of height.
Would anyone be saying that Araujo wasn't at a disadvantage because he had shorter than average arms? Or that Biyombo wouldn't be the prospect he is if he didn't have the wingspan and reach he did?