I don't think we have a clear ethic yet, for these situations. There's obviously a ton of economic power in platforms. Since the msft-vs-netscape days, it's been controversial.
Ultimately... these are marketplaces, important ones and, considering their size, scope and influence... I think there is a strong case that "my house, my rules" is not a reasonable way of doing things.
Apple/Google's app & content stores are huge bottlenecks and being locked out of them is on the same scale as being locked out of the financial/banking system for certain companies.
Does "free market" mean anything useful, if the free market consists of a handful of unfree "platforms?"
There's a similar question for FB and Twitter. They are such big media channels that being locked out of one could (for example) make it impossible to run for elected office.
Things have different implications at large scale.