Also mod_php was more akin to FastCGI with the limited access it gave PHP to the Apache request cycle. While mod_perl allowed you to effectively override any stage of the Apache request cycle with custom code. With mod_perl2 this was pushed to the point where I believe the Apache Foundation was running Apache for their SMTP servers running custom Perl protocol handlers.
Also mod_php was more akin to FastCGI with the limited access it gave PHP to the Apache request cycle. While mod_perl allowed you to effectively override any stage of the Apache request cycle with custom code. With mod_perl2 this was pushed to the point where I believe the Apache Foundation was running Apache for their SMTP servers running custom Perl protocol handlers.