This article would be fascinating if it weren't missing, like, the point. I'm guessing there is a correlational, rather than causational relationship here.
Ah - wait, here's an article that seems to care more:
Why circumcision should offer some protection is not well understood, but researchers know that the part of the foreskin that is removed in the operation is rich in Langerhans cells that the virus strongly attaches to. "HIV has to gain access to the body and to do that it binds to particular cell types," Dr Puren said. "By removing the skin that contains those cells, you remove the tissue the virus would normally bind to." Similar trials are ongoing in Kenya and Uganda and are expected to end within the next year.Of course, like, condoms probably work even better than just changing men's physical characteristics, but whatever. Do you think it will be easier to educate men to go under the knife than to use a condom? Or wait, is it one of those scare tactic things that makes safe sex suddenly look way more attractive?