Only about 1/4 of the player base is in the U.S. A majority of the rest is in Asia. Either way, they make a lot of $$.

Think of all the traffic Blizzard gets on their network. There's no amount of money that will make it failure-proof 24/7/365, especially with millions of users. Hardware failures, software glitches, human errors are all inevitable. And believe it or not, Blizzard is a LOT better at handling technical problems these days. I remember when servers would be down for a whole week