Very true, but the methods that the manufacturer used to calculate the effectiveness at reducing transmission probably only account for PIV sex between a man and a woman, rather than oral or anal sex between any combination of people. It's not so much "heterosexual" as it is the particular behavior that people engage in. Could they account for other sexual behaviors? Probably. Is it worth their time and effort and money? Probably not. Valtrex is used as effective suppressive therapy in people of various sexual orientations.