I don't think it's an American phenomenon for the most part, but perhaps a western one. The thing is, that in many other places, people also don't expect a couple to be the sole providers for a child. It is hard to not be child-centred when you do not have much help (or any) from family, or you cannot frequently obtain babysitting (due to cost or availability), or others refuse to participate in family-friendly activities.
In many places of the world (I am not American), we do not think the world revolves around our children - but at the same time, family and friends do not necessarily emphasize all activities as being adult-only. To me, it is sort of like the whole "adult-only wedding" concept that exists in many western cultures. To those of us who live in cultures where "my child is your child" (ie, my in-laws have just as much "reign" over my kids as I, the mother does), I can *sort of* see M&M's point in that they are stuck in a rock and a hard place.
They seem to wish to continue life "as normal" but also don't necessarily have the family or friend support to do so, and so are probably quite resentful that they are constrained in that manner.
Don't get me wrong, as I said before, I would never expect my friends to change their lifestyle/social life for me as a mother, but at the same time, my friends and family also accept babies and children as equals, in the sense that they deserve to participate as well.
It seems a western phenomenon IMO to even have to adjust from childless to parents because there is such a stark divide between the groups. If the children were never really excluded in the first place, would it still be narcissism?
The Chinese mother can leave her baby with her parents if she wants to go out. I have British friends who think it "pawning off".