Like everyone else is pointing out, flops are not measures of disk space. FLOP = floating point operations per second, i.e. a measure of CPU performance.
As for the daily cost of running a server, just do the math and see how much it costs a year.
$137k * 365 = $50 mil
Now consider that Wrath sold 2.8 mil copies just in the first 24 hours, not to mention how much it may have sold afterwards. That's at least:
2.8 mil * $40 = $112 mil
And since you mentioned 2010, Cataclysm launched at the tail end of 2010 to the tune of 4.7 million in the first month.
4.7 mil * $40 = $188 mil
So yeah, the server costs could be covered just by the box sales alone. Which makes you wonder, if you think your sub fee is covering the cost of accessing and keeping the server up, why are you being charged for the box price as well?
Imagine, if people weren't paying a sub fee for WoW, they might have to actually release content/expansions more frequently to cover the cost...