POSIX only covers the API's not the ABI's the software will run on. Also, that still leaves them running on a vendor specific CPU architecture. Your naive if y

POSIX only covers the API's not the ABI's the software will run on. Also, that still leaves them running on a vendor specific CPU architecture. Your naive if you believe Microsoft and Google don't hold all the cards with thier platforms. More and more of Android is being swallowed up by Google Play Services. Windows does have a central software repository called "Windows Store". Let's not forget about how users have to put up with thier shenanigans because they are the gatekeepers to apps.