Netflix may have lost more than simply some exclusive content when Epix signed a subscription streaming deal with Amazon. It may have lost the argument over a critical piece of its business model.

Reuters reported yesterday that Amazon had agreed to an escalator clause in its licensing deal with Epix, under which Amazon’s fee will increase as the number of subscribers to Amazon Prime Instant Video increases. That makes the terms more like cable TV, where distributors typically pay per-subscriber fees to carry a network’s programming, than like the DVD business, where the retailer pays once for the discs and then retains the upside for itself.

Netflix has long resisted the per-subscriber deal structure for its streaming business because it would effectively cap the retailer’s gross margins and could conflict with Netflix’s consumer proposition of all-you-can-eat for a flat fee. The studios, however, came to rue the initial deals they did with Netflix once they realized their content was helping increase Netflix’s subscriber base — and thus its revenue — without the content owner getting a taste of the upside.

Amazon isn’t the only subscription streaming service to have agreed to accept some sort of per-subscriber fee structure. According to Bloomberg, Redbox and Verizon will pay content owners fees based on the number of subscribers to the streaming service they plan to launch later this year.

Netflix has long maintained that per-subscriber licensing fees can’t work for an over-the-top streaming service, and that imposing it on a distributor  would make the business unprofitable, benefiting no one. If Amazon and Redbox are able to make a go of it, however, that argument may be lost forever.