I didn't. Your logic is built on the fallacy that the following are independent:
> An OS kernel, drivers, a browser (with a JavaScript compiler), a Java VM, all the applications (each one developed independently).
They aren't. The kernel and the drivers can't be built in parallel. You can only build the browser after you build the kernel and the driver (best-case scenario you can make the OS POSIX-compliant and begin to develop some of the userspace along, on another POSIX-compliant OS, but it's not trivial and there will be additional porting effort no matter what). Ditto for JVM, and you will have additional integration effort between the JVM and the browser.
> An OS kernel, drivers, a browser (with a JavaScript compiler), a Java VM, all the applications (each one developed independently).
They aren't. The kernel and the drivers can't be built in parallel. You can only build the browser after you build the kernel and the driver (best-case scenario you can make the OS POSIX-compliant and begin to develop some of the userspace along, on another POSIX-compliant OS, but it's not trivial and there will be additional porting effort no matter what). Ditto for JVM, and you will have additional integration effort between the JVM and the browser.