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. Tools like Embperl, Mason, and Apache::ASP all want to hand off control to a template immediately, which puts the templates in the driver's seat (i.e. it's more like a complete program than a template). The others require you to run some other program and just call the template tool when you want to generate output.
I wasn't trying to use these terms to separate tools which use in-line code from those that don't. For example, I don't call Text::Template a callback system.
I don't have a trademark on these terms and you're free to use them as you wish, or ignore them completely. I'm just explaining what I had in mind when I wrote that.