By a "Perl-only site", do you mean one where output is generated purely by code (either mod_perl handlers or scripts called via CGI, Apache::Registry, and so on?

If you think that's more maintainable than a template-based site, I think you're quite mistaken. What does a designer who only knows HTML do in a pure Perl environment? She makes HTML and hands it off to developers, who then have to break it into chunks and stick it in code.

I've seen that with a reasonably well-factored Mason-based site, HTML developers can learn pretty quickly not to touch the Mason parts, and are capable of making many changes without developer help. Major overhauls still require cooperation with the developers, but that's probably a good thing anyway. This means developers have more time to focus on real bug fixes and new features. How is that less maintainable?