The figures refer to what proportion of cleaning people are employed by a service that takes a cut. (She says 6 out of 7 are not. Her participation observation represents the work experience of the 1 out of 7 who are. IMHO, it should be generalized with that in mind.) The figure for pay ($20/hr) was taken from Wojtek's post, where he said the problem was not the rate of pay but the size of the services' cut. I said that of course for 6/7 who don't work for services, there is no such cut. I assumed that whatever the market rate, it would be the same for both. I was making no claims about what that rate was in general.
As for the rate of pay of domestics in New York, that's based on my asking everyone I knew how much they paid when I finally decided to hire someone. I knwo anyone who was paying less than $50 to get their apartment cleaned; the median was $60. In my case, it takes two hours. I'm sure other people's take longer. I was using those figures because this is the only market I know anything about personally.
As for comparisons to upstate, your figures make comparative sense. If I was a wordprocessor in upstate New York, I'd probably make between $10/hr myself. Here I make $35 and time and a half for overtime. Of course housing and food is comparatively more expensive here too, for both rich and poor. But some services are just better paid here because of higher demand and richer people to pay, and wordprocessing and homecleaning are probably two of them.
Michael