I don't think it's sexist to notice the fact that daughters, on the whole, have closer relationships with their mothers once grown up. I know this isn't true in each and every case, but on the whole, unfortunately, it is. In most cases, if the daughter has her own children, it will be her on maternity leave, choosing to spend time with her mother, (over mil) who will in turn form a closer bond with the grandchildren, and will be first port of call to help out as the children grow, and become an integral part of the family unit.
I know this isn't true in every case, but I'm just going on the 50+ sets of parents I know since having children, and on the whole, the maternal grandparents are included more, and closer to the family than the paternal grandparents are. There are obviously exceptions to this, some have moved far away etc, so naturally aren't as close. I'm one of 4, 2 girls, 2 boys, and me and my sister are far closer to my parents than my brother's. I speak with my mum daily, whereas my brother's will go months without speaking to my mum and not acknowledging her messages, for no reason other than the fact they're wrapped up in their own little worlds and just forget to make contact. My dh needs prompting from me everytime to call his parents, and most of my friends say the same about their husbands. I don't think it's sexist to notice this trend, it's just a fact of life. I feel immensely close to my mother since giving birth and becoming a mum myself, maybe because I now know how bloody hard it is, and have a huge new found respect for her. Something a man won't experience. I know becoming a father is hard work too, but (again generalising) on the whole, life changes far more for the new mother than the new father. I dunno, call me sexist, but this is just how it is in my experience. Not to say these trends won't change, but currently, this is how it is.