Things from BigVideo that would be varying degrees of PITA to roll your own, pending the browser support:
* measuring window size
* creating a slider slider component without full <input type=range support>
* having appropriate snap points on that slider
* event model normalization
* pub/sub
* detecting when an image asset has loaded
* $(body).prepend() equivalence: insertBefore() can throw if someone's HTML has a comment comment directly inside the body tag (typical with HTML5 Boilerplate code)
Sure it'd be
nice to have this be plain old JS, but as a developer you're signing up for a lot of pain that is merely just plumbing required to build your unique component. If BigVideo was targeting IE10 and everyone else, then we'd have a much better looking story in the code.