I don't know much about AVS/AEN sites and their situation with Visa. I recall they were on shaky ground awhile back. Visa had this idea that AVS sites were actually 3rd party processors for the sites under them and that those sites should be bound to the Visa regs (which frown upon the word boy). Could this have something to do with that?

If not, my money is still on confused surfers resulting in the ban of the word.

Sometimes it's not about sticking up for what is legal. The decision to ban something can be about unwanted attention. Among certain audiences, the word boy can cause confusion. Plain and simple.