Well, thats an excellent point.. and if SSIs wouldn't do, I could always use something like HTML::Template's TMPL_INCLUDE system to do the same thing.
However, there is an advantage to using the <script src=...> -- When you use it, you are allowed to include a host other then the one the original HTML file was loaded from. So if you're browser requests
pizza.html can contain the line:
I hope that made sense :-) I have a project that makes use of this sort of thing, called OpenThought. It's all about delivering content to a web browser without making the pages reload. The code will be in CVS within a day, and you can read the current documentation at the website.