well i try... (german here, my english isnt the best)
ping is using icmp protocol - this protocol is not neccessarly active by default... so if its not active the computer isnt answering on ping request but u can play with others.
well if u try to play with 2 peple try OpenVPN, this vpn software supports layer 2 vpn - so it also transmits broadcasts in the network - i tested it and it works very well with civ 5 for at least 2 players. with vpn programs like tungle or wippien i cant get a game running - sometimes its found but i never managed to join.
i also tried win2008 server with vpn but no success.
for openvpn i used:
vmware server - its free
openvpnas - its a ready running vm ware machine wich can be importet and started by vmware with some simple mouse clicks.
putty - small program to create accounts on the machine
well if firaxis dont manage to bring direktip to the game playing with steam leaves the only option for the most players.