I think it is a difference, to raise boys, and different for men in their minds when considering raising a boy vs. a girl.
My husband wanted all girls, didn't want any boys; but I think that was because he was afraid that he wouldn't be a good father to boys, but would be a good father to girls. Or maybe that he knew what it was like to *be* a boy, and thought girls would be easier, or have fewer problems or something. He never really verbalized why he wanted a girl. Then I got pregnant.
We both thought it was a boy, but he said he wanted a girl -- though he didn't belabor the point. Then we had an u/s a few weeks before I was due, and decided to find out the sex. It was a boy. I was a little nervous, because I thought he might be disappointed, since he had said he wanted a girl; but I have never seen him look so *joyous*! After we had him, my husband said, "I don't know why I ever wanted a girl! I want all boys -- a hockey team!" But I know that if we were to have a girl, he would be thrilled with her, and probably wonder why he ever wanted a boy. ;-)
Yes, I think there is a father-son dynamic that goes on that we women don't quite get, just like there is a father-daughter thing, and a mother-son and mother-daughter thing. With fathers and sons, though, there may be something about a man doing things with and for their sons that they felt were lacking or missing in their relationship with their own fathers. And, face it, males are all very similar, and have certain experiences which females do not have (testosterone levels, e.g.), and a man may feel that he is more able to relate to a son, even though he doesn't necessarily love or want a son more than a daughter, but just be able to *relate* to the son more.