That's O'Rourke's Law of Circumcision, that you can take 10% off the top of anything.
The question is though, is this actually a good idea? There's certainly some health benefits, as researchers in Africa are finding. It most certainly reduces the incidence of HIV.
However there are others who think that the decreased sensitivity of men after circumcision is a problem. But if you click through one of the links above you'll fin a very interesting argument which puts forward the proof that this is itself a good thing, now a downer.