By yours truly, on the GrowingDevs blog, giving you some more reasons and help on using Bower instead of RubyGems for managing your front-end assets in Rails:
Rails 4.0.4 depends on version 2.2.x of the jquery-rails gem which in turn bundles 1.9.1 of JQuery. Does that make any sense? The latest official release of angular-ui-bootstrap-rails is 0.9.0, which is at least a version behind the current release of the Angular UI bootstrap directives. When will it be updated? chosen-rails version 1.1.0 bundles an old version of chosen-jquery that has never been officially released. What?
The state of front-end assets in RubyGems is almost comical. Please start using Bower.