Yeah that's the thing, I think although some sons are close to their mother, and some daughters are not, there is this general train of thought from many, that the relationship will be better/closer with a daughter (when they are grown especially.)
I know loads of middle aged and older women who have much closer relationships with their adult daughters than they do with their adult sons. I mean, they go shopping, for lunch, for day trips, to the cinema, out to the park with the kids, etc etc. I don't know one woman who does this kind of stuff with their adult son; not one.
Also, I know many a couple who have daughters and many who have sons, and the bond with the children of their daughter, is much closer than it is with the children of their son.
I have a brother who has 2 kids (boys,) and I have 2 kids (girls,) and without a shadow of a doubt, my mother had a much closer relationship with my kids.
Mainly because she saw my kids at least once a week, and my brother's kids no more than 6 times a year. My brother and SIL rarely visited her, and often made excuses when she wanted to visit them. My SIL made sure HER parents saw the 2 kids a couple of times a week though, even though her parents lived the same distance from them, as mine and my brother's parents (about 10-12 miles away.)
My brother was also rarely arsed with my 2 kids, and only made an effort to see them on their birthdays, and a week before Christmas. He was much closer to his wife's brother's kids and saw them at least once a week, and took them on day trips, and out to theme parks and everything...
My brother and SIL's 2 boys are nearly grown now, and as they have 2 boys, I feel karma will come and bite them on the arse, as undoubtedly the grandmothers of their son's children will be closer to their grandchildren than they will to them.