gksu(do) is on the way out but as of yet common uses of using pkexec aren't in place. (gedit, nautilus, gdebi, ect.
So why it's not installed is unknown here, just another fault in what may just be an 'obligated' release
Anyway users will be prompted to install but should be aware that the default install mode of gksu is "su" which doesn't work out well in Ubuntu.
So after installing one must run (possibly only in 64 bit
And change the mode from su (screen) to sudo or you'll be prompted to provide the 'root' password instead of the admin user passwordCode:gksu-properties