I was talking about this with some of my (female) colleagues last week... all of who have 2 kids, max. My husband and I are aiming for 3, possibly 4, with the option of fostering after that.
One of my colleagues actually said 'if my husband did as much childcare as yours does, I'd have had more, but I couldn't take care of everything for more than 2 kids if I was the only one doing work!'
... not sure that extrapolates across North America, but I thought it was a perceptive statement... 'cause, honestly, a HUGE thing factoring into me wanting more kids is the fact that my husband is an incredibly involved father. 2am wake-ups needing an hour of rocking? He does 'em. Bathtime is usually a dad thing. He takes our daughter to her swim class. They play together. If I was the one doing all of it, HELLS NO would I be looking at more kids.
So: generational difference? Yes/no/maybe?
Some of it is generational. Some personality?
When my older son was born (10 years ago now), we had a new mom's/ new parent's group. Now, a fair number of us were between the ages of 35-40 (first kid). There was one mom who was 45. Pretty sure she did IVF, and I remember meeting her a couple of times at the doctor's office and in baby classes. Anyway, at one point, she was marveling at how involved our husbands were - and her husband didn't do much of anything with the baby. I said "honey, he's 60!! My father in law is 62! In his generation, men just didn't do much."
Even so, I'd say there are a handful of the dads from this group who like to spend their weekends watching sports on TV or going golfing, instead of being with the kids.
My younger son's group, it's more arrested development - a fair number of wives complain about coming home from work to find dirty diapers all over, and their husband sitting on the couch playing video games.
Also, working/ not working parents change the dynamic. I don't know anyone with 3+ kids where both parents work full time. Generally there is a SAHM, or one parent works part time.