Who is "Main Street"?

The continual reference to Main Street has been driving me crazy, so I was excited when I heard this on NPR.

http://www.npr.org/templates/story/story.php?storyId=95251612

A listener calls in and says:

"Main Street already went bust, remember the big box stores and suburban sprawl"

The listener then goes on to suggest some alternatives:

Wall Street and Your Street

Wall Street and Mall Street

I agree, there's no main street any more. Its a strip mall that you have to drive to from your 30,000 ft home in your 300ft Hummer.