This is not just in the programming business. Highly productive employees are generally underpaid relative to their peers. In his book, "Choosing the Right Pond", the economist Robert H. Frank attributes this to status-seeking. Short version: the highly paid employee could make more elsewhere, but then they wouldn't be the the big fish in the small pond anymore. On the flip side, the relatively low-productivity employee may be overpaid in compensation for the shame of being the worst programmer on the team.