My dentist charges for fillings per tooth
My doctor charges per medical procedure
My dry cleaner charges per garment

In fact, I think our consumer society is pretty well adapt at paying for a product per unit cost.

Mind you that UAL's recently announced policy is a last ditch effort on full flights and after every other effort has been made to accommodate the obese person (for free).

So, when an airline (no, make that 9 airlines) assert that a ticket price includes one seat as per the DOT carriage agreement, the rules of unit cost consumerism don't apply? I don't understand that logic.

I would say from a business standpoint it makes perfect sense. From a PR standpoint, now that is a problem.