All that stuff sounds really great if you had a lot of engineering resources and you are writing Gmail, but for 99% of the sites out there the JS hacks that load just the deltas and whatnot just get confused by packet loss and I end up having to reload the entire page including the gigantic JS hairball, or even worse the thing is so confused that I have to clear my cache and cookies to make it ever work again.

Simplicity has so many things in its favor.