System V init has been replaced by "upstart"

Upstream Deployment Guide:
http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/6/html/Technical_Notes/deployment.html

Fedora Wiki:
http://fedoraproject.org/wiki/Features/Upstart

Run levels are depreciated:
http://en.wikipedia.org/wiki/Runlevel
http://en.wikipedia.org/wiki/Upstart

This change has been in the works for a few years:
http://lists.centos.org/pipermail/centos/2009-September/082817.html

Some articles from Google search [RHEL centos upstart]
http://www.linux.com/archive/articles/57213
http://searchenterpriselinux.techtarget.com/tip/RHEL-6-ditches-System-V-init-for-Upstart-What-Linux-admins-need-to-know