'We acknowledge that some of our users require the use of works that do not conform to the Debian Free Software Guidelines. We have created "contrib" and "non-free" areas in our archive for these works. The packages in these areas are not part of the Debian system, although they have been configured for use with Debian.' -- http://www.fr.debian.org/social_contract
Maybe neither of us agrees with the resulting action, but I think that's an understandable, clear and obvious motive. The Debian OS itself is 100% free software nevertheless and the project doesn't develop proprietary software.
No, it isn't. It is quite irrelevant how much you quote the Social Contract. Go look at ftp.debian.org for a change, specially in the non-free and contrib directories. Infact, Debian does develop non-free software, since DD's who support the non-free section do exactly that, develop it.
I'd expect the debian project to be in GBN's contrib list, not GBN itself.
I expect GBN not to have a "contrib" list, since such a list will only recommend companies that do non-free software.