If you want to use .DEB and .RPM just look at 7zip:
It is an easy way to do it without scripting.
I am doing self extracting 7zip for windows and I am thinking about using 7zip for .deb packages too.
I am not going to worry about RPM unless a lot of people ask for it. If someone is using Fedora Desktop or SUSE they probably already know how to install .DEB's, thanks to the popularity of Ubuntu and other debian spinoff's.
I have a very strong feeling that SteamOS is either going to be a re-rolled Ubuntu, or Debian.