Exactly; for regular apps with little interaction needs, I start with a pure Rails back-end, and mix KnockOut.js only where relevant (for instance), or not at all.

For more UI-dynamic apps like https://www.wisecashhq.com, I go Rails JSON back-end + html rendering for skeleton, and KnockOut.js for the interactivity.

Now that DHH advocates "his way or the highway" isn't really a surprise :-)