I read all the statistics when I was applying to university a few years back, it was my high-school careers councillor who actually pointed it out to me. All the open-statistics give the percentages for university drop out rates (they all seem similar throughout the UK, Canada and Australia and many parts of Europe where I've read the statistics). The incomes I've actually only seen for the US, Canada and the UK, which all seem to correlate reasonably well, however nothing offers a reason for the unemployment of university drop outs.

In this context I believe the distinction is between a technical college (1-3 year programs for certifications and diplomas) and a degree-orientated/undergraduate university, where the courses typically grant a bachelors degree instead of certification or a diploma.

I have to note the UK's statistics on this front are very confusing, as there is no physical distinction between a technical college and a university as there is in North America and is based off of course-outcome aims rather than actual institutions attended.

Canada's statistics are rather interesting on university drop outs, in that the Atlantic Provinces have phenomenally low first-year drop out rates (I believe P.E.I. is ~16% versus ~36% in Ontario, note that these don't include first-year failure percentages). So it truly isn't the institution itself that causes the failure, but an artefact of the process present in most schools.