It doesn't matter what Rails decides to do if your HTTP server doesn't support it.
With that said, it looks like many do already support it (from the same article you linked): Apache, nginx, Phusion Passenger, Unicorn, Thin, and WEBrick.
Also, Rails supports an override as well, so you can send it as a POST but specify a different verb in a header, and it will treat it as a native request with the correct verb.
HTTP PUT is for in place entire entity updates. HTTP PATCH is for partial updates.
This isn't some opinion these guys came up with. It's HTTP standards.
Also if you don't like what save does. Write your own Backbone.sync and be done with it. Still super flexible.