Ability to defend is not solely determined by weight, but it is a big factor when you're guarding the post. Some people like Camby and Kirilenko overcome their weight disadvantage with superior skills. I haven't heard anything about Aldridge being one of those guys.
The point I'm trying to make is that Aldridge is not a center. Some SF's are heavier than him, most PF's are heavier than him, and pretty much all centers are. I just can't see drafting him to be your franchise center.
It seems like Steve Nash and the Suns have fooled fans into thinking that you don't need a center in today's NBA, and it's ok to put a mixed bag of forwards out on the floor, even if you don't have an elite point guard like Steve Nash.
I never thought that Aldridge was a center, but this new info about him being even lighter than we previously thought makes the idea stranger yet.