Eh? Blizzard developed their service for Warcraft II back in 1996, I don't see what WoW has to do with that.
Since 1996 it has expanded exponentially, most days over 500 thousand people are connected to battle.net. In 1996 Warcraft 2 was still a niche game with a (comparatively to today's standards)a small community. The complexity of the systems, the locals of the servers (all over the world) and having to deal with laws/regulations /staff//maintenance in todays climate is COMPLETELY different to 1996 mate and costs a fortune.
Yes the current p2p system they have in place in COH2 is a joke but if there was and is a better/ cheaper/ more efficient way to have people connected (from all global locations) I am sure they would be using it. Ok I put this question to everyone, would people be willing to pay 5-10 dollars a month to allow relic to maintain servers across the globe? The answer is probably not and given the relatively small player base playing this game that fee may need to be substantially higher.