I think in an ideal world, if I earned enough, I would probably pay a nanny of mine at roughly the same level as a primary school teacher, because I think the jobs have a lot in common. But unfortunately I am an academic, and I'm only earning at that sort of level myself, so after tax it has to be in proportion with what I earn. I've still got to run a house, feed the kids, get to work, keep myself in pants, pay something into a pension plan, insure myself and so on. In your 40s with kids in tow, your overheads are pretty high, in reality. A lot of the nannies around here are in their 20s so these realities haven't struck home yet.
I think I'm very typical - last time I looked, the high earners whom people on this thread and similar ones have referred to consitute a minute proportion of the population statistically speaking (less than 5%), but seem to get all the attention. It's unrealistic to base nanny salary calculations on the overall take home pay of such a tiny group of people, particularly with a recession looming.
It's got nothing to do with being mean or not valuing people. I am sure my employers would love to pay me more, because I do a great job, but I know there is no way they could afford it. It does not mean I am not valued.