Those sites aren't using Rails (edit: too heavily) either, which was the basis of comparison in the article.

Github/Twitter are massive with millions of visitors... they need to minimize every millisecond. It's not just about choosing the best developer-friendly or cleanest option.

Performance is #1.

That's not the case for the average smaller apps.

Frameworks like Backbone.js and Ember are growing very quicky and every open example app I've seen uses client-side templating.