Most people don't imagine they want those features until they see someone else in their social group using them – fancy status in the form of stories is a great example of this.

People have a strong desire to imitate and one-up others in their social group.

If you build a feature that even 1% of users self-start to use, then the social network can snow ball that with the right mechanics. And these feature need only be used by 20-30% of users for it to be considered a success. Every user is not expected to use all features.