Jacob Covey over at Fantagraphics is clearly a man after my own heart. This is basically the answer I was trying to come up with in response to a comment a few weeks back:
"[...] I know that nobody is viewing this cover and having these thoughts pop into their mind. For the record, I don't believe it's a conscious response that the book browser has to these things; I do believe there is an unconcscious response though. On my best day the goal is not to 'market' a book but to distill unconscious cues into evoking some story about the content in a single, eye-catching cover design..."