Which webserver is much better for production for RoR hosting?
for instance: mongrel versus apache2?
can mongrel does something which apache2 cannot ?
mongrel is definitely an application server, while Apache 2 is really a web server. They are not rivaling one another, but cooperating.
With that said, you need to ignore mongrel and go have a look at Phusion Passenger, that is a credit card applicatoin server which will use either Apache or Nginx (another web server).