I'm not a ruby user so I might be missing your point but...
There's nothing stopping you running php on a separate dedicated machine from the web server. You'd just use mod_fastcgi and php-fpm.
You can run it in a webserver thread (mod_php), run it in its own process alongside the webserver (mod_fcgid), run it on a dedicated machine (mod_fastcgi) or run it from the command line.
That's the beauty of PHP, it lets you do what you want. The downside is that this flexibility can be dangerous in inexperienced / naive hands.
Right, you can do what you want, I know that. The point is: If you do it, then you're at the deployment model that rails has been using all the time and that the php people said to be way too complicated. The simplest way nowadays to deploy rails is mod_passenger. It's about as simple as it gets - dump files, reload app. Done.
Actually, I don't get what's so simple about deploying PHP files individually via ftp. All I do is enter 'cap deploy' on a terminal. And I get free rollback. (there's web interfaces as well)
There's nothing stopping you running php on a separate dedicated machine from the web server. You'd just use mod_fastcgi and php-fpm.
You can run it in a webserver thread (mod_php), run it in its own process alongside the webserver (mod_fcgid), run it on a dedicated machine (mod_fastcgi) or run it from the command line.
That's the beauty of PHP, it lets you do what you want. The downside is that this flexibility can be dangerous in inexperienced / naive hands.