How does a long-awaited sequel, which became the fastest selling PC game of all time, still end up with a 2-star rating on Amazon? Probably because so many people were excited to play it and then couldn't, due to Blizzard's "always online" anti-piracy strategy combined with shaky server support.
Diablo III has made tons of money, but still turned into a PR nightmare for its parent company. From an economic perspective, however, these two things are not necessarily in opposition.
The newsvendor (or 'newsboy') problem, popular in the operations management literature, gives some insight into this apparent contradiction. It models a retailer who doesn't know exactly how much demand there will be for his/her product in the next period, and has to decide on inventory levels now. The vendor knows quantity demanded will be pulled from some statistical distribution, and wants to maximize expected profits.
This situation isn't too different from a video game company trying to decide how much to invest in server capacity. Blizzard doesn't know exactly how many people will buy the game on its release date, although they probably have some estimate (based on pre-purchases or past sales totals for their games, for example). They ideally want to have just enough server capacity to let everyone play, and no more. Given uncertainty, however, that goal is hard to accomplish.
The newsvendor model would advise a firm to purchase the average quantity demanded, assuming the costs of over- and under-purchase are exactly equal. For Diablo III, costs aren't exactly equal: once someone has bought, they won't be able to return the game if servers are overloaded -- at worst, maybe they tell friends not to buy it. But, if Blizzard over-purchases in server capacity, they're stuck with those costs.
In this case, over-purchase costs are higher than under-purchase costs, so it's rational for Blizzard to buy less than the average expected demand for their server capacity... Much to the chagrin of their loyal fans.
Consumers have a right to be annoyed, but these opening-day server issues shouldn't be much of a surprise. Counter-intuitively, if everyone could play without any interruptions at all, that outcome would probably be even more inefficient, at least from Blizzard's perspective.