My fiancee and I play WoW together, I introduced it to her, mainly to get her off my back for the hours I was putting in at the time. As time has progressed and we both got more into the game in general, it is her that is the "Hardcore" gamer when it comes to WoW, and it is I that is the "Casual". She beat me to level 80 and currently has 5 characters at that level, and is working on her 6th. All of which damage dealers, and all of which she prides herself on being able to "pwn" the dps tables. She was raiding long before I was. She frequently "rapes the shit" out of people in PvP. She also makes a huge amount of money at Auction with the various professions. She shows all the signs of male dominance that you describe, yet she lacks the genitals and testosterone.
Myself on the otherhand, I enjoy a bit of PvP, and tend to use my hunter as a crowd controler and harasser, I just take pleasure from pissing people off, but I dont PvP very often. I have a few 3 level 80's, a tank, a healer and a damage class. I enjoy being able to be responsible for more than just putting out epic numbers in DPS, I like to be able to control the pace of a run, or be responsible for keeping the group/raid alive. Thing is, I dont raid very often, maybe the weekly if its a quick run, and I perhaps do one dungeon a day for the frost emblems. I tend to spend most of my time exploring the worls, fishing, cooking, working the Auction House, but not anywhere near as successfully as her. I tend to work on my reputations, collect mounts, and generally achievement chase as I am a bit of a collector. I also tend to take my time leveling a lot more, fully completing zones, especially if they are zones I have never previously leveled in. I like to chill out and watch the grass grow a bit more.
Now in our relationship on the whole, I most definately "wear the trousers". I make the most money, make most of the cruicial decisions, after discussion of course, but I usually talk her round, and all the other cliche's of a male-female relationship. She tends to work out our finances, budgets for shopping etc etc. Our shared passion for gaming on the whole is what got us talking in the first place, yet she is a damn sight more competetive at it than me, and woe betide me if I should "own" her while playing (which to my delight i tend to do in PvP or duels).
We have a really great healthy relationship, and maybe its the role-reversal while playing WoW that cintributes to that.