Is google AJAX Libraries API bypassing same origin policy?

Question

From: https://developer.mozilla.org/En/Same_origin_policy_for_JavaScript

The same origin policy prevents a document or script loaded from one  
origin from getting or setting properties of a document from another origin.
This policy dates all the way back to Netscape Navigator 2.0.

So why is not the same origin policy enforced?, when a have a script tag like this:

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.min.js"></script>

I'm sure I'm missing 'something', I've read
http://code.google.com/p/browsersec/wiki/Part2#Same-origin_policy
a bunch of times but can not figure out...

Answer 1

HTML can load from wherever it likes, it's another script running on the page that can't fetch documents from another origin.

Answer 2

<script> tags are an exception to this rule. A page is allowed to "invite" a script from another server, and that's considered OK.

(The whole economy of the internet - on-page advertising - is based on this being allowed! Although it does represent a security risk, it's not going to change any time soon.)