FWIW, without doing, y'know actual research, I can remember *writing* two fics with money shots (one B7, one Firefly) and both of them were specifically in the context of space!porn flicks so it's a circle. The Circle of Smut! With antelopes and everything.

In a way, though, I've found slash to be counter-money-shot because the *instant* there's a drop of semen anyplace, the characters usually rush to the bathtub or shower to wash up.