I may be incorrect on this but, I have always thought that RedHat started their business to sell support for Linux, not necessarily their version of Linux. RedHat started with only one distribution, freely downloadable, and built their business on selling "official support" for that distribution.
At the time, I was running Slackware servers and will admit that I didn't really follow the reasoning behind Redhat's split into Fedora and RHEL. My guess was, without really following along, that RedHat decided to garner the cool system administration tools that made their distribution "enterprise ready" for themselves, and release and support Fedora freely onward.
If this is true, then I don't see why CentOS is in the wrong and/or hurting RHEL. Cent is not selling support for their distribution. Although, I've been to their website and read a bit. It IS kinda quirky how they refer to RedHat as "a prominent North American Enterprise Linux vendor." Almost like they feel like they are stealing.