In general, I understand the man - women are so good to bring the brains out, that I sometimes want to have a friend so hard to fuck! The most interesting thing is that his girlfriend liked it and she suggested that sometimes for a change in the relationship to apply such a role-playing game!
Well I do not know about the undeveloped ass, in my opinion a man very intensely and without preparation fucks a lady in the ass, and she gets a lot of pleasure out of it! So I think the ass is quite well developed.