ooh interesting question uwila (and a big assumption too?).
I know a couple (well, friends of my parents who had kids when older) who are millionnaires who always had live in au pairs, even though the mother doesn't work. I could never help myself looking down my nose a bit about it, esp when i was looking at their holiday photos and most of the ones of the kids were taken of them playing with the au pair! Hardly any family photos. (Used to wonder how the hell she thought me as a full time single SAHM coped!
But hey, if i won the lottery I wouldn't hesitate to probably hire a full time nanny at least, to be on call to babysit whenever I needed a lie in/night out etc! . And I'd still call myself a SAHM. And, I have to admit too that I don't actually know how many hours their au pairs worked! I'm just being a cow really.