How is it not an apt comparison? Is it any more ridiculous than thinking that buying a game years ago should somehow mean you should be able to stream it for free years later? Why? The reason Sony charges money for PSNow is because the bandwidth required for streaming costs money. Would it be amazing if they just ate the cost and let people do it? Sure. But do I also understand why they wouldn't? Yes. That's not what they were ever intending PSNow to be.
Because physical media and digital media aren't the same thing. Yeah, it's a lot more ridiculous considering the X1 is doing it for free currently. Then offer an upgraded tier PS+ tier or eat the cost with all the people playing on their TVs/Tablets since evidently few will take advantage of BC anyways.