Putting to one side the slightly shady way in which Facebook found out about this new start-up for a second, I have a question. There are examples of companies

Putting to one side the slightly shady way in which Facebook found out about this new start-up for a second, I have a question. There are examples of companies that made a success of focusing-in on one aspect of a larger successful company (e.g. the companies that split out the functionality of craigslist). But, this feels like an example of what happens when you mistake a Feature for a Business. How do you distinguish between the two cases?