It's a strategic acquisition. Such acquisitions are common, especially in the Valley. This is one reason why startups should primarily work to "make something people want" (the official Y Combinator motto) rather than focusing on making money. True, sometimes a startup achieves spectacular growth without ever finding a way to turn it into money, but examples are surprisingly rare. Can you think of any offhand? Maybe Twitter, but I'd bet they'll find a way to be hugely profitable someday.