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.
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.