I don't understand your first line: if real people don't care about keyboard navigation, why do we care what the keyboard navigation is for those people, and not for people who do use it? Power users use keyboard shortcuts, so make it work for them. Also, consistency is king in UI design, that doesn't change because we're talking about 'real people'.
We should care about backspace, specifically, because for the 99.9998% of the population that does not routinely use it for Back it is only a source of costly, frustrating errors.
"Consistency is king in UI design" gets mentioned in a lot of books. So do tarot cards. I don't have good experimental apparati for disproving tarot predictions but UI consistency has been judged in the A/B test crucible numerous times and frequently been found wanting.
Just a note, consistency is not always the king. Context is often more important, which is usually neglected by designers. Although I agree this is not the case, and no one should override browser shortcuts until he's got a killer reason for it.
