I've never had to forward ports for either FFXI or XIV--and I don't use PnP either. That's going back to around late 2005, with different brand name routers--Blitzz, Ativa (rebranded Belkin), and my current Netgear. May daughter facetimes on her ipod touch, while playing Elsword on her laptop, and I play XI or XIV on either my PC or my laptop. Never had issues with any of them because of my local network setup. These aren't high-end models either... I've never paid more than $40 for my routers at local retailers (not an ebay or amazon deal, I got them from brick and mortar stores). NAT has come a long way, and so long as your client is maintaining the session properly, it shouldn't be a problem. SE just puts that out there as a CYA sort of thing, as it does resolve issues with certain security models (like when stricter firewall rules are in place). The only time I've forwarded a port is for Torrent use or when I needed to RDP to my desktop from the outside--but never for XI/XIV. It's just one of those things for you to try to rule it out as a problem.

So, the port forwarding may or may not be needed--it depends on your particular situation.