While most of Google's services (and most SaaS providers) are closed, the web does enable freedom, and is still generally more open than the proprietary binary blobs people install onto their computers. Chromium is open source, Firefox is open source, and as long as the web itself is being advanced, we are more 'free', not locked into MS Windows, OSX, or even Linux or BSD.
Lets give up our freedoms to install programs, modify operating systems, write native code, use a programming language of choice, freely deploy native apps to users to get the freedom to consume media inside a browser sandbox.
Does developer mode come with a c/c++ compiler ? can you change the boot loader ? how about install a new shell ? replace the browser ? lets say you come up with a cool hack while in developer mode do you have to convince your friends to run in developer mode too ?
Chrome OS uses Gentoo's Portage package manager. So to install say, emacs, you simply do # emerge emacs, or whatever you want to install.
Anyhow, there's also plenty of online instructions on how to use Crouton to install Ubuntu onto Chrome OS, the point is that Chrome OS is a full, real Linux distro.
If it was endorsed by Google, you would have a user friendly way of doing that with full documentation, instead of hacks having to be explained by users via YouTube videos.
What rights do you give up by using an OS that is almost entirely open source? (keep in mind Linux has closed source parts too, some drivers for example)
If you dislike the paradigm that's fine, but don't claim it's hurting your freedom when
a) it's open source and
b) you can modify it the way you see fit.
Heck, you can change the Chromium OS source, recompile it and throw it on a Chromebook if you want...
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.
What free software? Locked down behind SaaS walls.