Do you think the other operating system camps don't use version control or something* ?
that would actually be mandatory, but as they are closed its a bit hard to guess how it looks like. with os4, since apparently there are distinct individuals who actually own their code, which is part of the os, it might well be, that this code isnt hosted in a common repo, but only binaries are being delivered for a release. sounds bothersome to maintain, but would explain, why it is so hard to gather and deliver an update, even if some issues have been fixed and tested for years, as some members claim. similarly thor has complained, that it was a long way to get at least majority of os components building within one build system.
one way or the other. i cant actually tell as im not involved. with aros the particular bauty is, that you can actually compile the whole os, contributions and many ports with just configure and make. yu just Need to choose the supported platforms and your desired flags.