Developing for a single platform and being able to run everywhere is great. I'm not sure what your "not possible elsewhere" is referring to, though. Java is one example of a language that's possible to deploy pretty much everywhere. Or do you mean natively in a browser?
While it's true that as a developer I'm free to use or not use any newly-introduced features and standards, as a consumer I don't have that choice. I either continue to use the sites and services I did before they changed everything, or I have to find an alternative which may not exist. Remember all the sites that required flash to run? That's what I want to avoid with responsive web apps.