The web browser _is_ the "safe" sandbox. Your dream of competing OS vendors coming together to build a standard UI platform makes no sense whatsoever. The current state of web apps is mostly a factor of developers being willing to do any amount of work whatsoever to avoid having to learn how to do things differently than they already know (ie, writing good native apps for multiple platforms, which would require learning multiple frameworks, so instead they create their own abstracted framework within a sandbox.