Investment pays off over time
I am a self-taught programmer who also got his diploma, and I agree the diploma doesn't help in terms of skills.
However, the comments about HR are true. The world's simply not fair and whining about it only makes the truth more painful.
Another scenario I saw more than once proves my point. The self-taught non-diploma guru reaches mid-life in a consulting company. He has a good reputation, maybe even manages some coders, but the new hires (with diplomas) make his salary starting out! This is especially true in sectors where jobs are contracted to the government. Allowable billed rates are based on measurable education levels, at least with the US government. Such people have a harder time going back to school because they have families, mortgages, and tuition is more expensive than it was 15-20 years prior.