Their thinking is that the inner mucosal foreskin is more susceptable to the virus. The flaw in their thinking is that there is always some inner mucosal foreskin left after circumcision. Usually 1/4 to 1/3 remains after circumcision. Couple that with the other methodological flaws in their "studies" and you will see that this "research" is nothing more than promoting an agenda to spread circumcision around the globe.
There are certain words that spread fear. At different times they have been Black Death (Bubonic Plague), tuberculosis, polio, masturbation and cancer. The latest is HIV/AIDS and I'm not surprised they have used this latest scare word in their promotion of male genital mutilation.