And it doesn't matter if i'm running it on a phone, tv, desktop, laptop, x86, ARM, windows, linux, mac, etc...

It removes all of those from the equation, web tech will be available on most platforms i want to use, so i'm free to choose the best for what i want without worrying if a ton of my software is supported.

Except all of those have vastly different methods of interacting with your web app. A responsive website can handle the more similar methods of interaction that a desktop, laptop, and mobile devices rely on with slight tweaks to account for a fingertip vs a mouse, but trying to run a similar application on a TV will be an exercise in user frustration.

I'm not saying you get magical interaction for free, but i've written a toy web app that works fine on my tv.

The arrow buttons on the remote act as up/down/left/right and the "OK" button acts as enter. It actually ended up needing very little in the way of custom code to work, but like i said this was a pretty small toy app.

Still, if you want an example of a real "web app" that runs on all of those platforms, just look at netflix.

Though in fairness, Netflix hasn't historically bee based on native web tech; it used to be Microsoft Silverlight for web browsers (I think they've gone/are going HTML5 now), and even now it's native apps for mobile devices/smart tvs/etc.

Consistent rendering of a webpage's contents across devices are not necessarily interlinked or dependent with the input methods.