I don't know. Companies like Amazon, Facebook and Google are obviously creating lots of new products/initiatives where revenue and scalability of the business model are still a big question mark. Is Facebook's core business scalable? Dunno.
Related question: Can you have a startup within a non-startup?
Only really if you want to argue that Facebooks business model is unsustainable. They're in profit now (I think?) so I'm pretty happy to say they're no longer a startup.
Related question: Can you have a startup within a non-startup?