Trust me, I say this as a developer, if there is any indication that I am losing out on users because I don't have Apple ID, I will make sure to add it asap. That is pretty much the reason why I first included FB and Google. I first only had Google, then some people aksed for FB. The natural course would have been that then some other guys ask for Apple and I add it. But Apple decided to abuse its position and force it on us developers