Support is expensive, but worth it. It's not unheard of to get custom kernel patches mere days after you reported an issue.
Well, that and the ecosystem of enterprise software which refuse to run on anything but RHEL.
And Ubuntu's failure to establish their home-grown stuff: Upstart, Unity, Mir, Ubuntu One, Ubuntu Phone, Juju...
That being said, 18.04 is a lot better than 12.04 or 14.04. I'm a Red Hat fan, but I hope Canonical succeeds - the more independent companies there are, the better.
Ubuntu doesn't really have that distinction. Shuttleworth is also kind of a character, and it's hard to rely on him keeping Ubuntu fixed on a particular use case. It's been desktop, then mobile/desktop convergence, and now containers and Kuberentes. Think startup vs big business.
The docs are just that much better. The server packages are much more reliable. If you want specific software versions, and you're not on docker, you get those versions. It's a breeze to sysadmin a centos machine. An Ubuntu machine is a pile of nightmares.
(Also, very few people actually run RHEL with the support package, most run CentOS, which is patch-compatible but has all the trademarks removed.)