I know that you can do a lot more with mod_perl than with mod_php.
But if I only want to generate content in a fast, memory persistent way, I don't need to step in and take over the other phases of a server response. Apache::Registry would be just perfect for this, and I don't agree that it is "a simple hack". Just because it's so easy to use it, doesn't mean that you can't build "real" web-sites with it.
The fact we only have a choice between very cheap cgi scripts (with all their drawbacks) and a very expensive swiss-army knife is annoying.