Well, shares are company value, not product value. And companies are valued by their ability to create value. A terrible decision usually doesn't mean much, and share price fluctuation is mainly speculative in nature. A large company may survive a bad CEO, and create value down the road. Even a crashing company has value, as it may be split and sold with a profit, turning shares into cash.

All in all, as much as I hate, EA for example, they have a strong position and can easily eat up failed releases for years to come. Many of their releases are payed off with only pre-orders.