Google Docs allows you to save to your harddrive. Indeed most office solutions should and they do.
The why of the web? Refalm mentioned one aspect. How about the ability to seemlessly access and edit all of your documents through one well-understood interface on your Windows work pc, your home mac or gnu/linux computer, your tablet, etc? Launch the URL and do what you need. How about the web is the most important information resource we have, and making it richer, while remaining very much backwards compatible whereever that's possible, will be an improvement making it simpler to create richer applications, while in fact making things faster? I basically think you're dissing the technology when you should perhaps turn your attention to the websites and web-developer decisions. The majority of professional web developers know too much about backwards compatibility in the sense of IE support and not in the sense of working on all types of configurations including super-slow computers (except mobiles), but you have to ask yourself what is
their interest in putting resources into those configurations, but I think the efforts of those designing the technology are pretty much as substantial as they can be for keeping the web accessible to everyone, as is indeed one of the motives of the web originally.
Just what we need, CPU-muching browsers that give us a slower, less useful, less worthwhile computer experience!
You can always use an old browser but in many cases this will
not make your web experience faster! this is due to the momentous efforts by many companies at making JS become the fastest interpreted language it can be.
You can disable JS and there may be pages on the web that should work better for people who have JS disabled, but that's between those people and the websites - not the technologies of the web! (which are substantial in areas of compatibility and accessibility)
HTML is still supported! In fact it's one of the only standards we can expect to be supported in 50 years time.
What about your Word files? What do you think those users are gonna do in 50 years time?
Gmail has a static interface option, other big email servers too. But other than that you have to ask where the demand for it is. Very few people do not use JS, I would argue that almost everyone bar people with serious resource limits should be turning it on.