[TheCoelacanth]

Courts will generally not second-guess the judgement of management, but they are obliged to act in the interest of their shareholders, primarily, because shareholders have the ability to fire the board of directors.

If someone who owned a share of Search Google managed to get a controlling interest in Ad Google and was operating it to benefit Search Google to the detriment of Ad Google's minority shareholders, that would be one of the rare cases where a court would intervene.