Doc,
Have you thought about a direct comparative piece between supermarkets and online intermediaries?
Ie as a readily accessible way for the general public to grasp what is going on online.
Along the lines of supermarkets serve to help customers first find products (the search function eg Google) then make purchases (Google pay) as one side of the market proposition, then the flip second side is to offer brands the ability to be found and then purchased.
Entry to the physical supermarket being free at the point of use, just like online services appear to be...
Though the real world is busy tracking customers via loyalty cards, payment cards and scan whilst shopping data capture devices of course, just like what the online intermediaries are doing via cookies and other means of tracking and correlation.
Guy