Regarding hero images:
My understanding is that it was a term that came out of the print design world (magazines, I'd guess) to describe a cover with a picture of a celebrity or "hero" with various headlines superimposed over top. From there, the term just found its way to the web.
Disclaimer: I tried to validate this by searching for it on google and only found other anecdotal evidence, so, take this explanation with a grain of salt.