MOVIES: I'm going to rectify certain inequities

I rewatched my Spider-Man DVD today (after a day of panic in which I thought I had lost it). Loved it, as always -- but there's still one thing that bugs (ha!) me about it:

Why does everyone call May Parker "Aunt May"??

Peter, I can understand. Technically, she is his aunt. You've got me there. But why Mary Jane? I mean, do you call your friends' relatives Aunt This and Uncle That and Cousin The Other? If so, why? (And what kind of name is "The Other"?)

And, strangest of all, why in the hell would Norman Osborn address her as Aunt May? He's a grown man, for crying in the night. A corporate giant, a titan of industry. Why would he refer to his son's roommate's aunt as if she were his own? Weird. Next to that, a radioactive spider doesn't sound all that implausible.