One of the reasons people go to university (UK) and college (?US) is not just to get the piece of paper. It's also to meet up with like minded people and build a network so that later in life you've got a helping hand.

This is why prestige universities/colleges are prestigious; not necessarily because the actual education is better but because you meet the right sort of people to help you out later in life. Knowing the right sort of people is what can double/triple/quadruple your lifetime income, you only need one lucky break and luck comes to those who make it.

A piece of paper is not gauranteed to increase your income, but statistically people who have those pieces of paper tend to earn more than people without.