instagram and whatsapp are already bought, and facebook does have plenty of revenue. Snapchat has started their business model, and they do at least have some revenue. (Certainly not profit, but revenue).

Any way you look at it, there are still more "real" companies than in 1999. And the rest, well it's not that surprising when startups fail. It's a thing that happens all the time. It's much different than tons and tons of public companies going out of business.