The interesting bit is that to make that count they really need a good operational plan with respect to their infrastructure.
I got a peek at their infrastructure early on because the company where I worked (Netapp) was trying to sell them filers for their Oracle instances which were running the game. And the game is essentially a ginormous database being updated constantly based on player actions. What we saw was a very complex (and expensive) infrastructure which was clearly built expediently. I would think that over time they would have been working to refine this to something more manageable (and cost effective).
Ultimately, there is a 'killer' persistent world infrastructure architecture for this sort of traffic. Would be a good research topic for a thesis I suspect.