Obviously Netflix will just pass the cost on to its subscribers (where else would they get the money from?). It's very unlikely they'd implement this as a surcharge for their Comcast subscribers only (I wish they would, but I expect their contract with Comcast prohibits it), they'll just absorb it into the single subscription price. So in fact non-Comcast customers will effectively be indirectly paying Comcast to subsidise other users' access.
From an engineer's point of view it's all baffling (Netflix and their customers are both paying for a certain amount of bandwidth, so where's the need for anything more?), but when you view it through the lens of capitalist incentives it all makes perfect sense.