Having been an escort for a number of years, Voyeuristic I think you are in a very small minority and probably have a very considerate boyfriend. Most of the girls that I worked with would never dream of doing anal, and those that do are mostly desperate for the money. It seems like your pleasure seems to be focussed very much on what your partner is getting out of it, maybe you haven't had the right vaginal and clitoral stimulation? I appreciate everyone is different, so fair enough if that's what gets you off - I'm just pointing out that the majority of women don't enjoy it because there is nothing there to enjoy as a direct sexual experience anyway - unless you get off on the sensation of having a shit really, or submission and pain involved in anal sex - which granted gets some people off.
However when indulging in anal frequently you just have to watch your sphincter doesn't become incompetent. Whereas vaginal muscles are made to go back to normal after being stretched, the anus only opens naturally when signals are sent to and from the brain signalling a need to empy your rectum of poo - when it's forced open by sex the tightly closed sphincter muscle isn't ready and therefore the open and shut mechanism can be damaged - especially if violent sex is involved. That's just biology that no one can argue with really.
Here is an article detailing the potential risks of anal sex:
http://corporateresourcecouncil.org/white_papers/Health_Risks.pdf
As I said each to their own - but the fact that anal sex does nothing for me ensures that I'm not willing to risk leaking my own shit by the time I'm 40 if I can help it.