Facebook's biggest shortcoming is that it appears to have no ability to roll out a new product. I would be much more impressed if Facebook were able to crush Instagram, Whats App or SnapChat. It certainly has the resources but apparently not the know-how.
I think you're definitely right that a non-arbitrary number of people fit that description, but I think most are likely similar to me in that I downloaded Instagram because my friends were on Instagram - If Facebook had created a photo sharing/editing app this good directly into their news feed, I kind of assume it would have been a hit. Who knows though...
