Not just that really, I think his point is more so that AOSP will not build and run for 99% of phones out there (i.e. non-Nexus phones). There's a lot of reverse engineering that goes on from people like CyanogenMod to make it work on other devices. Manufacturers release kernel source, as they must, but they rarely release other modifications they make for their own devices to even boot. There's a lot of stupidity in the Android "hacker" community (i.e. XDA) where people go around saying "X manufacturer doesn't release their sources, I'm boycotting X" when in reality, except for the Chinese OEMs they do release the source that they're required to release, it's just that 90% of the time that source is nowhere near enough to produce a build that you can run on your phone.