I've also seen cases where children are closer to their fathers than their mothers. It all depends on the kind of family and the time each parent has to spare for the children.
I've also come across severe cases where mothers abandon their children and the father is left to care for them, thus resulting in those children hating their mothers as they grow due to her absence.
As for me I'd say that the preference is not fixed but is completely dependent on the personality of each parent and how well they allow their children relate with them.