Just considering the number of HUGE houses that are being built around here (and everywhere) I would have thought that families with 10 to 12 kids was the norm. I recently discovered that many of these monster houses aren't even finished off up stairs and are inhabited by 2 people.
I have noticed this, too. A lot of smaller families have large houses, while our family of seven has a tiny house. I thought maybe if we had less children, we could have had a bigger house. Then I looked at my children and couldn't think of one of them I would not want to have.
One thing I noticed about large families. Unless there is a dysfunctional problem, the children with large families will have close friends for life. A few weeks ago my sister-in-law was talking about how close her family is. As an only child it's something I will never know.