Well the gist of that whole thread was that port forwarding doesn't matter for game consoles, just PC games. Maybe thats not the case though?
I thought the OP was comparing Xbox settings to PS3 settings. not Xbox to PC. And there not the same.
Xbox ports: http://support.microsoft.com/kb/908874
TCP 80
UDP 88
UDP 3074
TCP 3074
UDP 53
TCP 53
PS3 Ports: http://us.playstation.com/support/answer/index.htm?a_id=241
TCP Ports: 80, 443, 5223, and 10070 - 10080
UDP Ports: 3478, 3479, 3658, and 10070
TCP Ports: 80, 443, 5223
UDP Ports: 3478, 3479, 3658
As you can see, PS3 is more complicated. Routing for PC depends on the game. If the question is can you port forward for multiple xboxes? The answer is yes, because its based on the mac address of the unit. Two identicle Xboxes will have unique mac addresses. Im kind of tired, so perhaps I am missing the point.