* OS 1 finds a bug in Gnome, reports it and perhaps fixes it
* OS 2 benefits from pulling in the new code as well, fixing bugs
* OS 3 writes a driver for the camera and publishes it as part of their kernel
* OS 4 finds a bug in the camera driver they started using, publishes their fix
Yes, there's some overheard to running 25 projects. There's also a huge downfall to excluding 24 projects from contributing as first class members of the project. To boot, it's also a situation where the more contributions make the fixes contributed even more battle tested and beneficial.
tl;dr - OSS development styles don't map onto commercial development styles cleanly