(we are NOT in the same economic realm as these folks)
It has struck me how efficient economically it is to have more than 2-3 children. You already have the "stuff" like car seats, a crib, clothes, stroller, and likely a mini-van. Though I always chuckle at folks with 1 child who feel it imperative to own a car that holds 7.
On the other hand, having more than 2 children is harder. There is more work for a mother on a daily basis including tidying, laundry, breaking up arguments, potty accidents, dealing with sulky moods (children included), dishes, and baths. It means more years of changing diapers and nursing. Babies are wonderful, but lots of work. I certainly wouldn't advise someone to have another child simply because it was the trendy thing to do. If status is what you crave, get a $800 dog, not a soul that needs to be nurtured for a lifetime.
If you are a good mommy, not necessarily a competitive one, then certainly once you invest in all the equipment, it makes sense to keep producing warm, soft, smiling, kissable babies.