And I'm a GNU Purist, besides my wireless drivers (Which are in
contrib) I have no non-free packages installed on my system. Ubuntu
doesn't offer any differentiations between non-free packages and free
packages in their repositories, which upset me when I run my weekly
"vrms" to find that the program "unrar" was non-free. Of course now I
use the (Far inferior) unrar-free program, but I hated how Ubuntu had
no seperation between the repositories.
I think that non-free software go to restricted and to multiverse, while main and universe are pure.
I believe main and restricted are enabled by default, and that is why you ended up with unrar.
By the way, I use 7zip to uncompress rar (I don't know if it compresses rar, I have never tried, I I have no intention to compress to a non-free format.).