redhat vs debian/ubuntu system architecture (& not deb vs rpm)?

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http://unix.stackexchange.com – What are the key areas(except package management) where Fedora/RHEL/CentOS differ from Debian/Ubuntu Linux systems? I'm asking this from a newbie's perspective to the Linux admin world so that make a more informed choice. This not another .deb v/s .rpm question. :) thanks (HowTos)