I guess it's in Blizzards estimation that it's too closely related to multi level marketing to attempt it, fearing they'll risk a lawsuit. Note that it's probably more the fear of the cost of the lawsuit, rather than anything else, since they'll be highly unlikely to loose it, since it's fairly obvious that it isn't multi level marketing by definition of danish law (gaming hosts such as poker, casino often runs recruit a friend and affiliate programs which isn't against danish law). Most likely they just don't want to take any chances, which I guess is fair enough Danish readers can read up on the definition of multi level marketing ("pyramidespil") here:

http://www.forbrug.dk/klage/love/for...ngslinjer/mlm/