Things like the tests, docs, examples, etc are not required for the npm distribution, and thus only add to the weight of the module without any use. It would be nice if these were included in a .npmignore file - see https://npmjs.org/doc/developers.html#Keeping-files-out-of-your-package

In fact, for backbone the only useful files are the license, readme, package.json and backbone.js - all the rest can be added to the .npmignore file.