The major difference is that almost no one buys a playstation and xbox for their built in capabilities - the games are the major reason people want these devices. Yes, people stream netflix on them, but usually because it is convenient with their AV install, not because it is some major differentiator that other devices don't have. Whereas with smart phones, it is reasonable and common to never touch the app store. Or at least never touch non-free apps from the app store.

The statement is a slippery-slope, but it's not a fallacy. The concept of a monopoly is one we can agree on, and the exposure to the risk being described is a real one. What is to stop a monopoly deciding 30% becomes 40%? Not much.