I believe gmail is actually checking the email against others in the thread and hiding the portions that are being repeated (like the plug footer which is repeated at the bottom of each reply in the thread.)
As for mono spaced fonts, I find them more difficult to read. I really don't see why they should be the norm, except for possibly some odd reverence to computer tradition. /* PLUG: http://plug.org, #utah on irc.freenode.net * Unsubscribe: http://plug.org/mailman/options/plug */
