It's also not like there aren't weirdly calcified ideas about RP norms within sub-genres. Pern players who've only played Pern have different ideas of the "typical RP experience" than WoD players who've only played WoD, and so forth.
ETA: My RP experience on MUDs was pretty bad, but that's on the games I played, not the genre. I think I had more trouble wrapping my mind around the fact that there weren't coded objects than I did posing, when I tried MUSHing. You could say you were sitting in a chair if there wasn't a chair, zomg.