I think a lot of it has to do with the mind set of our times.
Me Me Me.
A friend told me a little one liner..
Women are like monkeys. They don't let go of one branch until another one is within reach. I thought about it for a second and found it to be pretty much fact from past relationships.
My folks married in their early twenties and I have never heard them yell or fight once. I'm sure they have their episodes when alone but I just think people these days are much different than older generations. Those statistics would be interesting to see.