Indeed, the success of Linux in the enterprise owes a lot to Red Hat, as they gave enterprises the sort of consistent, corporate-buzzword-compliant support agreements that removed a lot of the scariness that would otherwise impede use of Linux for "important" services.
It allowed ISVs to certify their software packages against a consistent OS built, hardware vendors to utiliza a long-term consistent driver interface, and end-users to not have to worry about upgrade cycles, sudden performance changes, and so on.
Basically it gave enterprises that had been dependent on Solaris and the like a comparable Linux alternative.
Due to the success of Ubuntu you have user/experts in small to medium sized companies that have 'given Linux a go' and got some good experience of Ubuntu. They might prefer the Ubuntu ways of doing things, e.g. the 'no root' security model, the modern, up to date packages (e.g. latest version of PHP), the ultra easy firewall and plenty else.
However, due to the perception that Red Hat is 'enterprise' and that small to medium companies re cheapskate, the CentOS rip-off gets specified by micro-managers because they have heard it is more 'enterprisey'. 'They know best' and go with the turgid CentOS regardless of whether any developers on the team would prefer something else.
You then have a lot of hosting companies pushing CentOS because they think it is more 'enterprisey' and what their customers want. Non-technical managers listen to them and then blame their team for any server problems.
Sure, if you know your way around Red Hat it is the greatest thing since Windows 3.0, you can get it to do what you want just fine. But, actually, if you are not an expert yet then very little about Red Hat is obvious. Far too many answers to common problems are guesswork in forum answers that you come across. Furthermore any serious claim to better security goes out the window as soon as you add random repositories that you might need just to get your work done.
Red Hat has had its day. CentOS has been a mere rip off of Red Hat and it has not added to the state of the art. I know it has its fans but I wish it would just go away.
"""Due to the success of Ubuntu you have users/experts in small to medium sized companies that have 'given Linux a go' and got some good experience of Ubuntu""". I'm sorry, but there are very few Linux professionals I've ever met I'd consider themselves "experts" who would recommend Ubuntu for their environment. Pretty much 0 except the one guy I work with on the board of Software in the Public Interest (nonprofit that runs Debian). Ubuntu did the smart thing and got onto the "cloud" bandwagon very early. As a result, Ubuntu is likely one of the more pervasive operating systems within that community. The cloud environment is a very small part of the entire Linux ecosystem and doesn't equate at _all_ with the high end "enterprise/hpc" industry. Don't believe me? Take a look yourself at the top 500 supercomputer breakdown by operating system. Exactly 0 Ubuntu clusters. Ubuntu with high end sans such as EMC/Hitachi/etc? Nope, it plays massive second fiddle to RHEL where those companies first certify their hardware for.
Ubuntu is better than Debian regarding security (almost exclusively from the excellent work of Kees Cook, who now works on security for the ChromeOS project at google and hardens the Linux kernel. However, it still can't hold a candle to the proactive security features of RHEL (and hence the awful cheapskate CentOS as you call it). Don't believe me? Look up the gcc stack smashing protector and fortify source patches. Look at the glibc canary code that also helps (in tandem with the gcc patches) to prevent buffer overflows, execshield (from Ingo Molnar, a redhat employee) before NX bits on cpus were super common, the first mainstream distribution of Linux to include a mandatory access control framework (SELinux) enabled by default. Are some of these features in Ubuntu now? Sure. Why? Because Redhat employees wrote them and got them into upstream software, which downstream distributions like Ubuntu which do precious little engineering have adopted.
CentOS is more enterprisey than Ubuntu. Why? Because it is based on the enterprise standard when it comes to Linux, Redhat Enterprise Linux. Ubuntu still sucks with big enterprise SAN gear, it also sucks with some of the more high end networking kit (infiniband on Ubuntu, possible, but a royal PITA and the vendors laugh at you), it is terrible for realtime stuff, but it is fantastic if you want the same interface on your desktop, tablet, and phone. If you don't know your way around Linux (your comment about not knowing your way around Redhat), perhaps you shouldn't be managing Linux servers and you're helping contribute to the list of botnet nodes due to not having a clue what you're doing? Again, I work on Linux fulltime and have for awhile, the major serious differences between Redhat and Ubuntu/Debian:
- /etc/network/interfaces vs /etc/sysconfig/network-scripts/ifcfg-*
- /etc/default vs /etc/sysconfig
- metapackages for everything vs yum groups
- dpkg/apt vs rpm/yum
- Building debs vs building rpms (I could rant for a day on how much ridiculously easier it is to build redhat packages)
- Preseed vs Kickstart (wth was Ian Murdoch thinking here? Preseed is still years behind kickstart in being awesome)
Sorry for the rant. It isn't normally my style, but this is just ridiculous. Feel free to downvote this, but please do some reading and learn Linux. You'll realize I'm likely right.
I have no idea why one arrangement of /etc/ is preferable to another, for example. Is it just security, isolation, and better package management?