Flat rate in the dial up era was a consequence of, among other things, a peculiar sort of regulatory arbitrage and an ability to leverage an existing network. But it set the standard for expectation in broadband.
There are, of course, likely economic consequences for the internet economy in a move to metered pricing. And it is rational to ask why the rest of the world seems to be doing faster flat rate than we can manage. But for that analysis I need more time than I have at the moment and will probably post on my professional blog.
UPDATE: You can see my professional blog post here: