What if he did have a big launch, with an app for android and a web version? What if it was a big failure and he lost more money than he made? Would that have made sense? This is a new product that he is testing the waters with. He chose the quickest and most effective way of doing this.

iOS is probably the easiest platform on which to do a subscription publication and reach a large audience. People are often unwilling to pay for subscription content on the web because they have to fill in a credit card form, and there can be problems with cancelling, and Android's subscription magazine thingy is US-only.