Yep. Because the game itself, the subscription fee along with 4 expansions with a 5th on the way is not enough of a pay wall.
From a business sense it's logical, I suppose, but only in the short term, people won't keep buying expansions if the design suffers (Now I await the morons who make a joke about CoD) and the design will suffer if they try and speed up production to that level.
This, however, is coming from a non-subscriber to WoW so maybe it makes more sense to them.
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And then there's EVE which comes out with two expansions a year for free, the latest of which deployed today.