The vast majority of the packages in Ubuntu (more notably in the LTS releases) are all custom patched by Ubu-devs. Rather than taking the raw package and pushing it through, they have a semi-opaque method of testing, patching, and then releasing to the greater community.
I've tried several times to get an 'in' so that I could help with the process, but it seems to me like a 'club hangout' where outsiders are slightly discouraged. :(
My experiences fixing the resulting brokenness and occasional unbootability is why I first claimed Ubuntu/Debian on my CV.