Not for servers. Which is what we're talking about.

I was a bit doubtful, so I looked it up... turns out you're only somewhat right: CentOS + RHEL are about 40% together (28.7% + 11.6% = 40.3), but Debian + Ubuntu are over 50% at (30.8% + 19.8% = 50.6). Arguably Debian is not Ubuntu (which is why I say you're somewhat right), but it is just what Ubuntu sysadmins grow up to, and has even more of a cool underground factor, despite being the most popular server distro. Of course RHEL and CentOS are the same thing as well.

Source: http://w3techs.com/technologies/details/os-linux/all/all (accuracy not entirely trusted, but it appears roughly accurate)

I have heard that there is a geographical difference where Redhat is more popular in North America while Debian is more popular in Europe. No idea if it is true though.