I really am focusing on the social elite of a small group of kids that I met over the summer. They're from California and I live on the East Coast (where Facebook is the norm). I'll be the first to admit that the plural of anecdote is not data. Which is why I said "some groups of people."
In any case, I think the difference in user population is because of accessibility to technology. Snapchat basically demands a swanky, whiz-bang phone, which not all kids have. I'd be willing to bet that more than 30% of kids (the difference in the statistics) lack a Snapchat-capable phone.
Being rich is cool, so apparently Snapchat is too. And it's cooler than Facebook, making Facebook uncool. I understand that there are a long list of logical fallacies in this section but hey, we're teens.