I'm glad you did the teardown because, despite the amount of people who are using any one of the MV* frameworks, few are authoritative on the differences/subtleties between.

Spine's "features", to a novice, are indistinguishable to Backbone's, which is probably what prompted the author's post.

In the world of Javascript frameworks, devs seem to pick a side based on the following:

1. Naming convention (Mootools' getStyle()+setStyle() vs. jQuery's css(), Router vs. Controller, etc.), which is admittedly personal preference.

2. Lowest barrier-to-entry (Spine.app, TodoMVC example)

3. Debugging (see: compiled Coffeescript lineno debate, compiled SCSS/LESS debate)