They do, in fact, have quite a bit of leeway. Eventually, though, when they need significant funding, or headcount, they ask their managers. As the project grows, it continues escalating, and if it's a major strategic commitment, it goes all the way up to the CEO and Board of Directors.

It's worked really, really well for Google thus far; have you seen the long-term trend of their stock price? Nonetheless, if you'd like to change it, you're welcome to acquire a controlling share of the company, and then you can run it however you please.