Has Everyone Forgotten About Income Tax?

Tuition fee stupidity:

Vince Cable, the Business Secretary, confirmed that ministers were examining ways to make the new system more "progressive". He said: "High-earning graduates will be paying more later in their life, but in a progressive way relating to their ability to pay. There is an issue about people who go on to very high-earning jobs and who therefore pay off relatively quickly and we do have to think about how to find a way by which they make some sort of contribution towards low-earning graduates. It's a tricky technical problem but we're working on it" 

Higher earners pay more income tax (not only more but at a higher rate too). "Tricky technical problem" already solved.

They Already Do

David Willetts, the Universities Minister, is quoted by The Telegraph as saying:

"Many young people aspire to go to university. On average it boosts your earnings by £100,000 over a lifetime. So, when money is tight, it is right to expect people to make a substantial contribution towards the cost of their university education – not when they are studying but afterwards when they are graduates on a decent income."

They already do, though. Has Mr Willets not heard of income tax?