Dear haveacrush:
I'll give this a stab - I feel that one should be careful about applying generalities to a gender specific behavior. Having been fortunate enough to live in San Francisco for many years, I knew many women who much more "butch" than either Jack or Ennis, and conversely, many men who were much more feminine than either Alma or Lureen. And almost all of them were happy to be just who they were. As has been pointed out frequently in earlier posts, sexuality (and sexual behavior) is pretty much a sliding scale for both hetero and homo sexual beings.
Personally, I feel this is one aspect of the film that (as you say) makes it resonate so emotionally with so many, the inside and deeply personal view of the back-and-forth between dominant and submissive roles that we see evolve. Both men play both roles, either directly or indirectly on screen. And to some degree this is part of the struggle we see, a male becoming comfortable in both roles. This may be part of the reason it resonates with females, as in our current culture females seem to be required (if not demanded) to plays both these roles more often than men. I'm thinking of single mothers who must nurture their young while working, running a household, and paying the bills. Men are much less likely to be put into this dual role, it happens, but nowhere near as frequently. Maybe women enjoy seeing how a male struggles and learns to do what they have been through. Not because they enjoy seeing his pain, but because they have a kinship with his struggle and his pain and emotional growth.
JMHO