Port Forwarding is not as easy as it seems.
People who have worked with computers and/or really know what they are doing think that port forwarding is the easiest thing ever. And it is, to them.
Most average people don't really know how to port forward, which is why Badspot gave a link to a tutorial. However, problems still come up. There are many people that still have trouble with port forwarding, and they aren't all people who own Macs.