> The kernel is nowadays 75% coded by paid programmers at huge corporations

It's even more than 80% contributed by paid programmers, according to the latest report from 1½ years ago:

http://www.linuxfoundation.org/news-media/announcements/2015/02/linux-foundation-releases-linux-development-report

> who need a good kernel for their server and server service needs.

...or their non-server needs (Linaro, Samsung, Texas Instruments, Vision Engraving Systems, Renesas etc.) :-)

> Ubuntu [...], and a lot of popular distros are made out of that codebase,
> by paid developers.

Are you sure that the official Ubuntu-based distributions are done by paid people? I only found that Kubuntu is contributed to also by corporate programmers, but not for the other distros.