Trader Joe's customers can and do shop at other stores as well. Whereas people don't realistically carry more than one phone or switch phone types frequently.

Trader Joes has what, 1% of the market share of shoppers? Android and iPhone have what, 99%?

How is 1% market share relevant? If that policy is justified, then market share is irrelevant.

... because a seller literally has 99% of the market to go after instead because they don't have a policy like that?

Going back to the grocery store analogy... https://en.wikipedia.org/wiki/List_of_supermarket_chains_in_...

While at least 50% of the random grocery stores you would see are under one of the big 5 (or so) many of these stores are generally able to carry additional products not even necessarily approved by the top. Part of that is simply competition with local chains. And that doesn't even cover the fact that you have gobs of local and regional chains to contact and sell goods to.

But basically as a seller of lemonade you are highly likely to be able to sell your product without insane restrictions - as well have the ability to choose a chain or store that has competitive markup or a markup that you agree with.

If you sell phone applications you are dealing with exactly 2 entities that you HAVE to go through.

Combined, not each.

If you can just define a market to whatever you want, then everyone has a 100% market share. By your definition, Samsung has a 100% market share on Samsung TVs.

No, because you can substitute a different manufacturer's TV for a Samsung one and vice versa.