alt Hacker NewsI'd be curious to know what portion of that 40% makes any meaningful income from their open source work. I would guess that most of those people are being paid a small appreciation amount for the work they're doing, not something resembling a living wage.
They may be including maintainers who are explicitly employed to maintain the respective projects (e.g. some RedHat employees). This is not common, but not vanishingly rare either.