Perl 6 huh?
Tsk, and I just bought the 5.12 camel book.
Mercifully it's a lot slimmer than my previous 5.x version (5.8 or maybe 5.6?) version -- which my nephew appears to have 'borrowed'.
I agree this site is predominantly PHP/.NET - not even Ruby has made a dent in that.
I think the problems for Perl are a perceived clunkiness in CGI programming - it's okay once you get your head round it and processing can be seperated from presentation.
After that, mod_perl programming starts to talk about server 'stuff' e.g. request phases, because mod_perl was written to exploit the Apache server for speed and quick response under heavy load. This is generally an area most PHP programmers do not want to know too much about.
You need control of your Apache configuration and Perl modules installation - something not usually offered by fasthosts, 123, godaddy and the like in the past - although far more widely available through the Virtual Host Systems now available through the likes of bytemark and others.
You basically need to know more to use mod_perl. mod_php installs and allows you to embed php into HTML straight away. On the outside this is far easier but php4 had some security issues with register_globals. The Shuhosin patch may make php safer.
From an employers viewpoint, there appear to be more php programmers than perl programmers which means they have more flexibility in whom they employ for less pay. So someone quits they have a larger pool to find a replacement.
Larger, global, very high traffic installations (bbc, ebuyer, amazon) favour mod_perl because they are global and high traffic. I suspect PHP doesn't handle that scenario so well but it is okay for the average, low traffic site.
I suspect PHP is also popular with people who don't have Comp Sci degrees.
All I know at the moment is Perl 6 is hugely different to Perl 5.