Please, there's web caching, app manifests, and all sorts of other ways and standards to create web apps which run 100% on the user's machine. Applications need not be behind an SaaS wall anymore than video games need online DRM....
And Chrome OS absolutely IS an OS. The fact that it's centred conceptually around the Chromium browser and Google's proprietary bits doesn't make this less true.
All applications are behind SaaS walls.