Thomcult: The online petition is a curious example of consumer activism. Invariably, consumers express their satisfaction (or lack thereof) through their choice to purchase. Firms are, generally speaking, able to ascertain whether their offering has at least appeared to satisfy the desires and demands of consumers by whether they have purchased it. If a company makes a bad game, or markets it badly, the expectations of consumers won't be met, they won't feel satisfied and as such it will fail in the marketplace.
When consumers go out of their way to express dissatisfaction with a product (at any point in its life cycle), when they do it en masse and in a medium of their own design it says something profound about their desire. By petitioning for changes in Diablo III's art direction these gamers are saying that they wish they did want Diablo, and are showing Blizzard that it's not beyond their remit to make them, yet at this point in time they do not. Of course, there is no talk of a mass boycott however the message this petition sends out is that the product Blizzard have currently shown is not the one they were expecting, nor the one they want.