Supercell is one of hundreds of developers on the App Store trying to make freemium mobile games.

They're doing well because they picked a winning business model for their games and then they went on to make great games. Clash of Clans was a breath of fresh air in an environment with tons of clones and uninspired crap. Also, entertainment is a hits driven business where if a product starts winning, it tends to dominate.

Picking a business model is crucial, but not sufficient, to be successful.