Users are free to use the mobile browser on their phones but most of the time native apps are a better experience. And guess who develops the framework and tools to create these value-adding native apps.
This is the free market at work.
The free market sometimes leads to a not-so-free market, which is ultimately bad for consumers. This is the entire reason there is anti-trust law.
I am not saying that there are current or even future anti-trust issues with app stores. I was simply using that analogy to illustrate that the "free market" can move in a direction that is less free to an extent that is negative for consumers. This can happen because consumers are free to choose.
In other words, that anti-trust laws exist and have been employed to combat this is simply offered as evidence that the great-grandparent post above overlooks the fact that the free market can lead to reduced choice for consumers.