Back when mobile gambling started, there were big differences in which casinos you could play in and what games were available. One of the major issues in those days was that Flash technology wasn't available on Apple devices and most slots were made with Flash.
Nowadays, the situation has completely changed. With the advent of HTML5, all mobile devices are equal. The same games work on all devices and everyone gets to play. So, it doesn't matter anymore if you have an Apple or an Android.