I don't know if this is priviledged information, or if it's entirely accurate, so take it with a grain of salt.
At midway, if a project breaks even/ goes platinum, everyone that worked on the project gets a royalty. Royalties start at the tippy-top of production (producers and project leads I believe), then trickle down from there. Royalties are given as a lump-some to central groups, which include UI design and music.
So... at least at Midway, the musicians do (unless they are outsourced, and often times they are). So you just got fucking pwn3d.