I think the format is designed to seat an eclectic mix of guests-you-wouldn't-normally-see-sharing-a-sofa together, in order to provoke an unexpected and off-beat mix of chat and banter amongst opposites. All overseen by the comic "puppetmaster" that is cheeky Graham.
However, I like your theory far more, so let's go with it... It's obviously the work of an evil cabal involving BBC Satanists, the Illuminati and possibly MI5 & Prince Philip.