Yes, for my distro SYS, I compile / recompile for my distro sometimes the kernel, mesa, the X system: www.copaya.yi.org/tgz (in opposite to a lot of distros which copy them from debian or somewhere else).
And the normal is, that the manufacturers of grafic cards would deliver source code for mesa.
But what I wanted to say with my post is, that, even when they don't want to deliver the source code, but binary code, then at least should be this the mesa driver, what one can copy into the corresponding subdirectory, i.e. within the normal schema , without that one would have to desinstall mesa because openGL is another (like this is the problem with nvidia drivers). I don't want to mess my distro, so manufacturers which don't want to observe the norms how and where openGL/mesa binaries for drivers have to be, maintainers of distros should not support them