- mod_perl has access to the apache api and hooks for each phase of a request
- fastcgi is basically a scheduler for perl server programs that communicate with the web server via sockets, so the only coupling between apache and fastcgi is on the I/O layer
OTOH AIUI mod_perl is an apache thing, while as you say, FastCGI has to do with "communicate with the web server via sockets", where "the web server" is not necessarily bound to be apache, and indeed I've heard very very good comments from web-dev-knowledgeable people about LightTPD in these respects.
