Pretty much this...They are basing their percentages on a survey of 381 online gamers. This is a far cry from the 10.3million that actually play WoW but probably can't be bothered to do a survey. Surveys are also notorious for being filled out by those people with time, or an axe to grind.
Now, this is a standard amount for a survey. but many of these "Online gamers" will probably be hardcore fans who demand X and Y, and were probably going to buy SWTOR anyways.The majority of people usually cannot be bothered, that's why psychologists simply try not to rely on that data alone. Remember this is all speculative. The people *may* say they will buy another game or quit WoW, but how many people do you know have said they will quit but never do?
It really cannot be used as any form of evidence until the decline actually happens, as unlike most MMOs, WoWs core base is the more casual gamer who frankly couldn't give two stuffs about which shiny new game is coming out, and even if they do, they will probably just carry on playing WoW as well. It is very easy to skew the results here tbh, whilst the percentages may look incredibly impressive, only a very naive person would take them as guaranteed.
I can see Blizzards stock price taking a very healthy increase over the next year though once MoP comes out and Diablo 3.