Why?
"Also, if Microsoft's "exorbitant licensing fees" have a "highly detrimental anticompetitive effect" on the market, as Barnes & Noble asserts, why are HTC and Amazon – which, as reported in their filing, have licensing agreements with Microsoft – doing so well in their respective smartphone and e-reader markets?"
You already answered your own question.
"These types of disputes tend to be settled in corporate conference rooms, with chunks of change changing hands."
The first few get it cheap, then they use the list of people who paid as proof that their claim must be good so you better pay too.