I dont think anyone is arguing Google Earth should be pure HTML. But it is equally false you cant do Gmail with HTML only.
There are things that HTML could do, and should be doing, that is not done or not yet possible simply due to hype and trend from browser vendors. We could continue to polish HTML + sprinkle of Javascript to its absolute maximum before hitting JS Apps. Right now this is far from the case.
Gmail used to provide an HTML version. It got removed only recently
Actually, I do think that. Wouldn't it be lovely to have an image format for truly enormous images and have the browser request only the chunk currently visible? It could just be a container format with jpg's in it. Let the file system figure out that x/y means tile number 56436.
You could provide multiple image versions for zooming to get to the TB scale.
Computers are really good, performance is astonishing, no reason why we should never be able to use a TB size image. Never is a really long time.
Have epic panoramas, detailed scans from paintings, extremely easy game design and maps that just work.
Gmail with html only would not be a nice experience. Modern gmail is really bloated but it's actually one of the few web apps I have no problems with.