Even in PHP you want that for decent performance: php-fpm is similar in concept to a Ruby/Python application server, albeit slightly different due to PHP being a web language first and foremost, and it's interesting execution method. Still, you run a process and connect nginx to it :)

Even for PHP you do, it's just delivered as an apache module. (Passenger can be run as an apache module too, fwiw).

Although to be fair, the PHP model doesn't require a _persistent_ process between requests (I think?). But most other platforms do.

It isn't required for Ruby either, but loading a Rails app is slow so it's better to persist it between requests.

Unless you also need high density multi-tenancy in which case you probably want to use mpm-itk for security..