That's actually a bit of a myth; companies don't have any explicit legal obligation to maximize shareholder value. In addition, courts tend to defer to their judgment on things such as intangibles; if a company says they're doing X because it's good for the company's image even though it loses money in the short term, a court will generally not second-guess that decision, especially since the shareholders have alternate means to reverse it if they disagree, such as voting out the board. To the extent the shareholders keep the board in place, they're presumed to agree with their decisions on where to take the company. The material that makes for a successful shareholder lawsuit tends to be more about things like favoring one class of shareholders over another, or executives making decisions for their personal gain.

Earlier HN discussion: http://news.ycombinator.com/item?id=3227980