No, Mac OS X is incredibly capable right out of the box.
With the regular Mac OS X you would be able to host multiple websites, act as a file server, have remote control, and run PHP, mySQL, etc. All of this can be done with no extra cost. But now that Lion Server has been released, it is just $30 to upgrade to the Server version.
There are also a lot of third party applications under $20 that will help you set up mail servers, databases, TFTP servers, and just about anything else you’d want to do.