Here is my made up guess: The average university graduate will do better without degree than the current non-grad averages.

You are making the assumption that it all boils down to the degree (the difference in income). This can't be possible (maybe a majority of it, but not all of it). There are other factors (like being from a middle-class, higher IQ, etc.) that selects for going to Uni. and this has effect later on income.