Average wage has very little to do with it, at least when it comes to London. People there pay a lot more than the rest of the country, but they're earning a lot more too. And even within London the same kind of logic applies.
Partly those people's wages rise. But more commonly they live elsewhere. Those people's wages have no connection to the house prices in zone 1, because those people live further out and commute.
Really: there has to be a limit.