Well, I certainly have nothing to back it up but I would think the 13" MBP outsells the 15" & 17" varieties, no? I know the white book is #1 overall.
13" MBP outsold every other shipping Mac at one point, though I get the feeling that time has since past, especially with these new MacBook Airs being somewhat of a hit. (They even look like thin 13" Pros for cryin' out loud!)
13.3" seems to be Apple's sweet spot otherwise they wouldn't have introduced another one.
Not necessarily; it makes sense to have one 13.3" laptop that is full featured, and then another that is an ultra-portable. Two that are full featured? Especially when the 13" Pro is essentially the successor of the middle and high-end configuration MacBooks of yesteryear?
do the math and see what going from a 16:10 display in the MBP to 16:9 measures out to be while keeping the same width. (I'm too lazy). Of course that means it won't be as deep. Is there room to do this?
I don't think it makes sense to even do that unless you make a larger bezel (as to keep machine depth and not sacrifice more), but at that point, why not have pixels on it?