> It's far easier to make a cut at "no logic apart from boolean checks" and then use a proper client-side framework such as backbone (...)

That works if you are fine with offsetting all (or most) of your presentation logic to client side. But not every web application is the glorified single-page web app, or has significant amount of on-page interaction that would warrant employing a full stack MVC framework on the client side.

> Templates should be about how things look like.

But also what elements are those things built from. Despite attempts at logic-less templates, the presentation layer still must contain some logic and I see no reason to not apply normal coding principles - most notably DRY - to that logic. That's why I consider it very important for a templating engine to allow for reusing things, and splitting things into parts. Here's where some engines really shine (Jinja immediately comes to mind, followed by Underscore or jQuery templates) and others... not so much.