Why not give the consumer the option to choose between wired or wireless.... after all any wired connection is far more stable than any wireless or bluetooth connection for that matter.
In my opinion the P4 should be compatible with the LAN expansion card. If @Jerel is correct and it isn't then thats a bad call on GHL. Unless there is a good reason why it wasn't made compatible. "Everybody having WiFi" is not a good reason. I mean the doser 2.1 has a LAN card and WiFi so.....
Technically GHL does give you an option.. It's not a part of the current design scheme, but it's a robust controller and somewhat future proof.