What I was trying to get at when I chose the terms callback and pipeline was the difference in how web requests are typically processed.
Yes, what you wrote was a system architect's document. And you also wrote the document in the context of processing web requests. This is definitely fair game for an article on a mod_perl website, but in my eyes, pipeline and callback apply more accurately to web application systems.
CGI::Application is pure pipeline... and regardless of what templating system you choose (even the ones you label callback), it will be used in the manner that you describe for pipeline systems.
Now on the other hand, HTML::Embperl and HTML::Mason (the system, not the template language) are pure callback systems.
Templating could be discussed without bring the web into it and then we could truly see how the execution model of template systems varies... hmm, sounds like a new node to me.