A Distro (short for distribution) is a version of the Linux/Unix operating system bundled together. Which Distro the system administrator selects is largely dependent on the data center hosting the box and what they provide and support. This page provides some general info about the the currently supported distros and gives those who have a choice some more information to help make a decision.
When RedHat discontinued the RedHat Linux line it switched official support exclusively to Red Hat Enterprise Linux, RHEL is a COMMERCIAL product
which means that you have to purchase it with a paid subscription. RHEL comes in several versions depending on your needs and budget. RHEL is designed
to run web servers and is an excellent product if you are willing to pay for it. It is very stable and rock solid. Some DC's do not charge extra for it
and include the licensing fee with your server rental.
"CentOS is an Enterprise-class Linux Distribution derived from sources freely provided to the public by a prominent North American Enterprise Linux vendor. CentOS conforms fully with the upstream vendors redistribution policy and aims to be 100% binary compatible. (CentOS mainly changes packages to remove upstream vendor branding and artwork.) CentOS is free." (from the CentOS website).
For each major release, the source code must be acquired, the necessary (generally minor) changes made, and the rpms created. Then they must be extensively tested and tweaked before they can officially be considered supported. In some cases changes to InterWorx itself must be made but at the same time the developers need to make sure that these changes do not break anything on one of the other supported distros because the core InterWorx rpm's are not distro specific.
The speed at which we support these Distributions is based on the demand. Most major hosting companies seem to prefer RPM-based distributions such as Red Hat EL and CentOS so for now our focus is primarily concerned with those.
CentOS is a clone of RHEL and the two are 100% binary compatible. What that means is that RPM's created for RHEL work on CentOS and vice versa. CentOS rpm's even incorporate the rhel into the filenames. Our CentOS rpm repository is actually a symlink to our RHEL repository on the updates server.