This all goes back to the "black men are hung huge" stereotype. That's all a bunch of bull, just like all Italians are huge, or French are huge, etc. There are little Black dudes, there are little Italian guys, and on and on and on. Every race will have big guys and small ones. It all depends on your genetica make up. People want to think because someone might be famous and/or cute that they are going to be hung, but it doesn't work that way. Celebrities fall into the same percentiles that the rest of society does. If they come from a family with big dick genes, they will probably be hung, if not, well...then they won't be.
According to some things I've read on the net, Usher is very average. I don't know about Kanye West. I saw when Usher pulled his pants down, and I didn't see any huge bulge. People need to get over the Star=Hung mentality.