You're saying that buying fake followers accounts for a 360 million user discrepancy (from 10%-30%)? Only a small subset of app developers, page maintainers, etc, buy fake followers, and most people are not app developers. And FB deletes fake accounts all the time. 6-12% is much more realistic than 30%. Most apps/networks have between 2-10% fake/dupe/invalid accounts, and you become a bigger target the larger you get.