It isn't that it is inadequate (CGI/Perl, that is), but rather that many applications may not need mod_perl. A simple guestbook, file manager, calendar, etc... may not need the speed enhancements, caching, response/logging phase massaging, etc... that mod_perl provides. mod_perl does add some bloat, which isn't always needed.

People need to do things with the right tools, and mod_perl is Just Another Tool. It is also a valuable tool which provides functionalities which 'regular' CGI/Perl does not. Or at least provides a more efficient way to do some things (for example, you *can* write to the http log file with CGI/Perl, but mod_perl provides a better way).

Whenever speed/response time is an issue with a CGI application, you should take mod_perl (or fastCGI) into account and see if those tools will help build a better web application.

Cheers,
KM