Remove generated JavaScript from your pages

One of the things that have always seemed a little weird to me is that ASP.NET auto-generates JavaScript and injects it in the rendered HTML. The JavaScript is needed to handle validation, postbacks, callbacks etc. but why does it have to write the same static functions when it could just as well be placed in a referenced .js file? If all the static functions where placed in an external .js file, it would be downloaded once instead of every time a page loads.