http://lwn.net/Articles/592723/

"So the goal for CentOS is to create a next-generation platform that
is supported for a longer period of time than Fedora is. Ten years
would be good, but most people just want something longer than 13
months, he said, and *2–3 YEARS SEEMED TO BE A SWEET SPOT*."

(emphasis added by me).

Pertinent question: are SL users "most people" ?