I don't think it is as easy as it sounds, you need to write much more code to handle that. And the code to handle that can't be in Java itself because you can't use Java to install the JVM, so you would need to build installers for each platform that you want to support.
For web applications, users don't need to install anything, they just open a link and see your program. Remember that a lot of people don't even know how to install software on their machines.
But sometimes you can reach "as fast as", for example using asm.js.
We already have Python, Lua and some others: http://repl.it/
There's even a JVM implemented in JS, but I haven't tested it, I don't know how many features it implements: http://int3.github.io/doppio/