Why does this require asynchronous GA and jQuery in the head?When a browser hits a script tag it waits (blocks) while it downloads the script and evaluates it. As such, including a bigger library like jQuery in the <head> will slow your perceived page load time significantly, so moving such includes to just before </body> is often a best practice. This way the browser can go ahead and render the page, and add the Javascript once its done.
However, this introduces the possibility that the user will see and click a link before the Javascript (on which the event tracking depends) has loaded. In this case Google Analytics will not track the event.
So by adding the Javascript includes to <head> he's forcing the browser to have Google Analytics running before the page is rendered, ensuring that this can't happen (at the expense of page load time).
I would not recommend taking this advice. As Travis pointed out, the event binding can easily be written without jQuery, giving the best of both worlds.
However, its a good article and this has little to do with the central point.