It is not very difficult task to ask google search about how many key-developers receives their paychecks from RedHat and IBM and how many of them contributing to Fedora project.
Then you can try to figure out how many installations of RHEL around, in the worlds biggest datacenters and then which distro amazon or google uses.
Then you can take a look on RedHat's revenue.
At last, if you're really curious, you can download .src.rpm of the latest CentOS kernel and take a look to the patches.
and very last hint: Oracle. DB2.