This was a thought I had the other day. As a city becomes more wealthy and grows and with ever larger companies forming / coming to the city, the city becomes more wealthy. This drives up the cost of housing to the point where while the on paper the average person makes much more money than in a smaller city. Any increase in wealth gets effectively absorbed by landlords and increasing property taxes. Making it more difficult and competitive for the average non tech non finance worker to be able to live there. In the end it seems kind of pointless? A lot of cities could very well be better off being composed of mostly traditional jobs. Baristas, barbers etc rather than these higher paying jobs.
This fun city nerd video is somewhat relevant: www.youtube.com/watch?v=IsbkvsyN-O8 Cities where the lowest percent of median income goes to median (housing + transportation). The winners were Seattle and San Francisco. This suggests that salaries may be able to compensate for increased housing costs. Of course, a longitudinal study would be necessary to answer this question.
Anecdotally, as a Seattlite, this is very much the case.