I don't think Google Maps does any heavy lifting and number-crunching in javascript in the browser; in fact, all it does in js is "remote out the UI part".
Let web-browsers remain good at what they're good at, and what they were meant for: Browsing the web. Web browsers make great hypermedia navigation / browsing tools... but they're really not so great at being the universal standard remote client interface for complex applications. :-(
