Beyond a certain market share, that argument doesn't hold anymore. That's where anti-trust comes in.

Which market share definition, you ask? IMHO it is the definition that defines decision making for app developers, on whether they can skip the Apple platform or not.

So Apple's percentage of global smartphones doesn't matter, what matters is:

- Apple's 2/3 share of app store revenues.

- Apple's share of users in rich, developed markets such as US, Europe and Japan, which (source: ben-evans.com) varies between ~50-70%.

It is unaffordable for app developers to skip the Apple platform, since that's where the majority of paying users are. And as a result, they should fall under anti-trust laws that protect small players.