I think it's almost like a competitiveness between the guys in the house.
I noticed once my (half) brother got older (13-14 years old) my step dad and him started fighting and arguing over pointless things.
On the other hand, my sisters have always been close to my step father.
My brother is/ has always been close with my mother, because he is the only son in the house hold, it's almost like their competing for my mothers love/ attention, even though she loves/ respects us all the same.
My step dad insists on laying down the law with my brother, but my sisters could almost get away with anything. (I stayed in my room most of my time living home, hardly talking to anyone in the house. I mainly observed.)
Sometimes I think my step dad was only strict with my brother because he wanted him to be respectful of women and to act like a kind young gentleman. (Which, now, he is respectful to everyone and is a gentleman to his girlfriends, and respects his friends and their family.)
My brother would probably much rather hang out with my mom than his dad because my mom was very laid back with him and never raised her voice with him. I think both parents love their children all the same, but the parents reactions to their kids misbehaiving, or even behaiving, reflects who their children would rather be with.
So I think why daughters hang out with their fathers more and why mothers hang on with ther sons more, is simply because of competitivness also, oppisites attract.