First off, I don't know about anyone else, but I did not assume that you meant 'one man, multiple wives' when I answered, Pixagi. I stated that I wanted a wife because that's my preference. One man is hard enough to deal with (no offense 'Trae ) I wouldn't know what to do with more than one (except for teh sex part - )!
What it boils down to for me is the desire for another companion. Someone to keep me company while 'Trae is at work and to help me out with the house and the kids. A little snuggle once in a while is simply a bonus.
Of course, the sharing thing would still be a problem for me. The only way I could see it working (again for me) would be if there were another man involved, i.e., two couples - one household. Realistically, everyone would have to get along well and play nice together.
Again, it's not so much about the sex for me, but rather the companionship. We are, after all, social creatures by nature.