for me the reason to stay with an apache/mod_php backend was very bad experience I had with fastcgi back in the 2006/2007 area where I was using a lighttpd/fastcgi configuration.

I've seen crashes in lighty, crashes in fastcgi and subtle differences in behavior between fastcgi and mod_php.

FastCGI just wasn't a commonly used method of deployment back then, so there were for sure some bugs around that I didn't have time or interest to fix.

By now, there's PHP-FPM and fastcgi is much more common, so you could probably just hook php directly into nginx by now, but I didn't want to do experiments and I knew that apache worked, so that's what I used.

Just remember to turn off keep-alive in apache, btw.