Yes and No. PHP (Perl for Home Pages) main starting point for popularity was that it was easy to make into an Apache module that could be used on shared hosting. Perl's Apache module was a single interpreter for the whole server. Great for business sites and such, not good when you have multiple unrelated users using the same server. PHP was just something that you could turn on and uses on your shared hosting.
According to Wikipedia PHP stands for "Personal Home Page".
Yes, the memory isolation model of mod_php was the crucial factor in beating the competition. With mod_perl you had to write your Perl modules to a specification so that globals were not accessible by other hosts. That was too much of a risk for shared hosting providers. The situation is muddied, however, in that a lot of shared hosts only allow PHP as a cgi which, in theory, puts it on a level playing-field with Perl. However, in practice, Perl only has one PHP-alike templating framework - HTML::Mason - and that requires mod_perl to perform decently. So PHP's other advantage is that its templating engine is simply faster.
