How many people buy Amazon Prime for the video streaming? What percentage of the $800M Prime revenue is attributable to the video service?
I'd wager less than 10%. Does Netflix spend more than $80M a year on AWS?
The numbers needed to answer the question aren't publicly available. It's a bunch of guesswork.
They spent $1.3B on "General/Administrative Expenses" last year - think more than 6% of that was infrastructure?
Especially on bandwidth, anyone can buy bandwidth at well below 20% of AWS prices elsewhere. Netflix shouldn't be paying even 10% of published AWS bandwidth prices given their volumes.
Previous to this arrangement Netflix used 3rd party CDNs like Akamai which again did not sit on Amazon's infrastructure.
That said I'm not agreeing or disagreeing with any assessment of how much Amazon costs are.
If the customers don't want TV they are put on a free tier rather than being cancelled, so they are still officially a TV subscriber and can boost the viewing figures for the service.
It's useful to be vague if you are in a dying industry or your competitors are better established.