If kernel-source is missing I need do add some (AFAICS large) parts of
the kernel-source package to each package im creating myself (e.g. for
an NTFS or DVB-Modules RPM-Package someone might create ;-) ). Thats a
large overhead there.
note that with exception of NTFS, the reason we disable a module is
generally because it is really really broken, so you wouldn't WANT to
use the source from that tree but some other, supposedly fixed, version
instead.