Japan actually prohibits porn distribution without censoring, so if you wanna put videos out there, you'll have to cover them dicks because, well, that's where the porn is.
As for the idea of moaning, being an Asian man (though not Japanese) myself, i'd say it because of the culture where in a gay couple, the bottom is viewed as the "wife. I have seen couples calling each other husband and…...wife and it is more common than you'd think.
So if you've seen (try, some guys are really sexy) regular Japanese porn with the girls moaning like no tomorrow, gay porn is pretty much the same but with guys.