Wealth, on a scale of being in the single digits percentage-wise, often has a lot to do with skill. Some skills, such as empire building, get you there faster than others. See Bill Gates as an example. First he built a tech empire, then a charitable empire. The man is very good at enacting world wide change.

Secondly, 5% producing 99% sounds very reasonable. If you ever have the misfortune of having to work with code written by contracted companies, you would realize a LOT of code is slapped together with no care at all. The average person contributing to open source or participating on hacker news cares. The average person coding is looking for a paycheck, and doesn't give a single damn.