> Of course if you load a bunch of code beforehand your code will be marginally better.

That's exactly the point though. We use jQuery because it has an incredible easy and consistent interface that makes writing for the web so much more enjoyable. Selectors, events, chaining,... are all just nicer to work with than the vanilla counterparts. Same goes for all libraries and frameworks. :)

BTW: Your example is sending a "multipart/form-data". Not all API's will understand this, and will need JSON anyway.