Most companies like to think that they don't have any "bad" projects; if they did, they would cancel them. And, they're afraid that employees will confuse "hard" projects with "bad" projects, and try to flee the hard projects, which are often business-critical.
Google is smart enough to realize that employees can often identify bad (and good) projects before the management does, and lets them vote with their feet.
My friend used to work for a large multi-national. In his company, each of the departments were like companies in itself. The formalities for quitting the job and changing departments were the same. So most of the time the only way to get off a bad project was to quit the company.
That's how I've usually heard of it being done at large companies. When a friend changed departments internally at a large petrochemicals company, he had to go through a whole application process: look on the internal HR system for a job opening, send in an application and resume, interview with the new group, etc.
It seems like a terrible waste if the only way to get off a bad project is to quit the company.