> Also, we make Backbone, $ and _ globals so we don't have to inject them in every single module.

We don't; we explicitly define every dependency, always, so that it does not make any assumptions about the environment it runs in (a webpage with jquery / underscore included via script tags, for example). Second, our end-product is a single .js with Backbone and some other dependencies all combined into it. (we're not allowed to use a CDN)