Backbone has some of the clearest, most self-explanatory source of any project I've ever worked on. Also, at around 1500 lines of commented code it's a quick read that you can take in all at once (and again later). Also, make sure to read the source in the master branch as well as the annotated docs from the website to keep you informed on the upcoming changes.
I'm not saying that you shouldn't read tutorials, guides, and docs, but you should concentrate most of your effort on taking in the source.
At first glance it seems that template rendering is a key point here (render-as-a-string vs. dom-manipulation). However, if you change the backbone implementation to use dom manipulation (http://jsfiddle.net/jqSK2/) it performs just as well (or better, depending on the browser). Backbone's event system is much more important in this comparison.
I'm not saying that you shouldn't read tutorials, guides, and docs, but you should concentrate most of your effort on taking in the source.