The time when it was possible to build simple application with good design and get tons of users is over. Today, a lot of people can do what the pioneers have done and get 0 users. I don't say it's impossible to get so many users as FB, but it's much harder. So Zuck was lucky to have the right solution in the right time. The bar for Zuck of today is much higher, simply because they aren't so "lucky" to live in the wild beginning of computer/ internet era.