That's quite a generalization. I program in both Perl and PHP -- Perl at home, for freelancing, and at work for primarily systems scripts that require text processing; PHP at work for web applications.

The decision to use PHP for web applications was made before I came, but I feel the reasons were sound: rapid prototyping; ability to create robust applications quickly and easily after prototyping; good and fast database abstraction layer (via PEAR); many programmers available should we need to outsource; and more.

As for me, I like the fact that to add a session to a PHP script, I simply start it with 'session_start()'; accessing POST, GET, COOKIE, and SESSION variables is intuitive and fairly secure (if you program correctly); and sometimes it's just so much easier to embed the HTML into the script (though I try and avoid that -- I like to separate content from layout).

I like perl for its robustness, and its extensibility -- I cannot do anonymous routines in PHP, for instance, which often bothers me, and I'll NEVER do any sort of systems or networking work with PHP -- and how easy it is to separate HTML from the scripted backend (HTML::Template and Template::Toolkit are excellent tools). But it's also easy for me to write code that others have trouble debugging; not so in PHP (whether or not that's a bonus is another question altogether).

Perl and PHP are both excellent tools; use each where they make sense.