I think there could be multiple reasons for it Deftone.
Every couple/relationship is different but I too have noticed this.
Years ago whenever I would here about a long term couple splitting, it was always deemed the man's fault, either he was caught cheating, bored of the wife and wanted a younger model or not their for the family... but always the man's fault.
Since I've been married, and especially since I started punting, I been on many forums and met quite a few middle aged married men that are struggling in relationships and all seems to point to the same reasons of lack of respect, acknowledgement as to what he brings to the family, and almost always lack of sex. A man's needs in modern relationships are no longer a priority,
My wife was telling me the other day, that one of her married, best friends, early 30's are getting divorced with a young child, and going through splitting the house. We don't see them often because they live 3 hours away but we stayed over last summer and I remember a conversation popping up about them not sleeping in the same bed for the last 6 months and my first thought was another sexless marriage...
In fact in our small circle of friends, we know of 5-6 couples with kids that are apparently struggling, (this is wife/girls talking) and with all of them it's the man's fault, not doing enough, not there emotionally..
Again back to every relationship is different but in my relationship, I have been accused of not doing enough, I tell myself I must do better but then I think, since being married, I've given up all of my hobbies I had before I met my wife, I would say I no longer have friends as I don't have time for them, I'm up at 4:45 every morning, walking the dogs, get home, help get the kid ready for school before heading to work, which with travel is a 10-11 hour day of physical work, go straight home, to interact with the kid for a further 3 hours before getting them down to bed, when they've finally gone down, load the dishwasher, shoes back on, walking the dogs again till gone 21:00 and rinse and repeat 5 days a week. If in that time I ever attempt to get some attention from the wife is met with annoyance and a reason why she can't do anything that day.
Does make me wonder what percentage of wives/partners with kids out there withhold sex once they know they hold all the cards in the relationship.
"Happy wife, happy life" is the biggest load of bollocks out there!