It's a communication platform that the younger generations are using as their primary form of communication. That is big.. not saying it's $10B big, but SnapChat has the chance to become something larger than just stupid selfies.
Edit: I am deeply skeptical that a market filled primarily with people who have little or no income will support an ad-based revenue stream valued at $10bn. I would be even more skeptical if the revenue for SnapChat were supposed to come from a pricing structure.
I myself have migrated my primary messaging platform through half that list. Isn't there a tremendous risk snapchat users leave that platform the way users have moved from one messaging platform to another for years?