This is true, but as others stated an over-simplification of Twitter's features. Even without the factor of scale, building Twitter for 1000 users would be hard

This is true, but as others stated an over-simplification of Twitter's features. Even without the factor of scale, building Twitter for 1000 users would be hard when you consider things like private messages, e-mail notifications, on-site notifications, hash tags, retweets, favoriting, follower-lists, url shorteners, images / videos, ads, analytics, search, security, new features like their 'moments' tab, - and considering how all of these features work together on mobile as well as web. THEN start thinking about scale and how these features work together - not just the C and R of CRUD, but the U and D too.