The thing is, I cannot rely on a variety of modules. A good majority of users don't have the experience/knowledge to install modules or they are not on a host that will install them. The CGI module is quite powerful but it is very big as well. Back when I first went commercial there was an offshoot of the GPL'd code that ported everything over to using CGI.pm. Eventually they had to pull this out because it started to bog down heavily on moderate traffic.
By no means am I saying PERL is not good enough. I still develop many of programs at work in PERL where I have control of the environment, but on a broadscale basis PHP doesn't require anything extra to be installed.
