It's not about if devices are general computing devices or if the device maker can moderate third-party apps on its platform. Apple invited other developers to sell apps on a market it created and regulates. It also competes with those developers in this market. And in this case, it used its power as the market's regulator to remove a competitor and promote its own app.
Nintendo, Sony, etc also allow other developers to sell apps on markets they created, and they also compete with those developers. If Nintendo ever removes a platforming game for competing with the Mario series, we should also raise our pitchforks and protest against unfair abuse of power.