Gamasutra has received an interesting stat from the good folks at NPD: after hearing that The Sims 3 sold over 800,000 copies in its first month, they were curious to see what kind of unit sales our own World of Warcraft has experienced. And the numbers are pretty big: among the original game and all of the expansion packs since the vanilla release over four years ago, NPD says 8.6 million boxes of WoW have been sold in the US. That's a little misleading if you're comparing it to actual subscription numbers: remember that this is over three different releases (so the actual number of all-time players, not current players, is probably 1/3 of that), and it includes different collectors' editions of each of the three game editions. So there are nowhere near 8.6 million US players of WoW -- that's just how many times players have come through the retail line with the various releases.
What that is, however, is a lot of money. Gamasutra estimates that at an average of $30 for each unit sold (the vanilla game currently retails at $20, but the expansions all sell at $40, and of course the original game was more expensive once upon a time), that's $258 million in income for Blizzard. In short, Blizzard's making a mint at the retail counter, even before they sign anyone up for subscriptions.
Then again, if you look at their own costs, those aren't insubstantial, either -- Activision's Bobby Kotick claimed that anyone starting up an MMO to compete with WoW would have to throw at least half a billion dollars into the mix just to get started, so we can presume Blizzard has spent at least $500 million on their staff, development, and hardware. So it's not like they're taking it all to the bank, though we can at least presume they're sitting firmly in the black.