ubuntu codenames are helpful in looking for technical assistance online. '20' isn't a particularly unique term online.
Because if you search for "Debian 6 foo", you should only be seeing results that contain that exact phrase (on Google, anyways).
This being said, I'm not using a distro that discards a version every 6 months, so I don't need to keep a 'continually scrolling' list of codewords in my head.