This whole "reduced likelihood" of transmission is bogus because, hopefully, sex isn't something that happes just once and, if you missed your transmission opportunity you are safe. Rather, sex is something couples have on a continuing basis with multiple exposure possibilities.
Let's say, theoretically, we have an HIV status discordant heterosexual couple and the female is HIV positive and the male is uncircumcised. They live together for a year and have sex one hundred times. If we arbitrarily say that 10% of coitus results in transmission from female to male, he got infected ten times. If we say that circumcision reduces transmission by 90% to 1% of sexual intercourse (highly doubtful), he still got infected. After this year of living together he is still infected even if he was circumcised. Meanwhile, circumsicion of males does not protect women from transission, at all, except indirectly in the form of theoretically lower prevalence of infection in males. I really have to doubt whether circumcision has any effect on the LIFETIME risk of transmission of HIV.
On the other hand, use of safer sex practices confers a high degree of protection to both partners.
Dave