It is illegal only when Apple owns the majority of the market share, that is, a monopoly. When iPhone users constituted more than 90% of all smart phone users,

It is illegal only when Apple owns the majority of the market share, that is, a monopoly. When iPhone users constituted more than 90% of all smart phone users, such practice would be illegal. Right now, Apple can argue that a tight controlled App Store is vital to their success, and any consumer who disagrees can simply switch to their competitor, Android.