I never said that Jenna Haze had a big ass, but she is a lot of fun to watch. Belladonna has a big ass, and is fairly slim. I really enjoyed watching Ryan Conner, and her ass was spectacular. Heck, even April Flowers back when really had a nice ass. For a tall woman, at about 6', Lauren Phoenix had a great ass and was incredibly energetic and enthusiastic during her scenes.
There is an abundance of average sized guys in porn, and that goes for all races. I think even though porn is embellished there are a LARGE percentage of average sized guys in porn on the whole. If you ever watch most Vivid or Wicked features you won't see any massively hung guys, at least not very often, because they want to appear to the "average" joe schmoe who happens to be average in EVERY way. For me that's one of the reasons that I stick to gonzo, because they usually employ a more well "rounded" male in their films, someone who can get a girl into a scene and is also pretty well endowed.