The current Kirk Tuck blog post has explained it all. He quotes a book that reviews psychological tests showing how once you have purchased an object, it becomes your personal choice of object, and its perceived value (to you) is greater than the value of any similar or even identical object. Evolution favors those with this attribute. His take on the serious GAS sufferer over multiple years and models:
Multi-system owners? Either they want to have the right tool at hand for a specific job or, more credibly they are trying to cover all of their bases so they can enhance their perceived safety and ranking in their tribe.
scott (owner of three systems plus a few film cameras, in case film comes back...)