Last time I checked, iOS has about 14% market share, while Android has 79%... Especially for something meant to be by proximity only, you'd want the highest chance of it being on the phones of people nearby... heh. Instead, this gets released on iOS only. Good luck with that.
But aren't iOS users most likely to spend money? Thus making them the perfect users to target if you're eventually going to show ads, or rent their information, or monetize in any way?
Yep. iOS users tend to spend more, in general. Think of this in the context of the specific application, though.
This is a proximity-based messaging. Without people nearby with the app, you have no one to talk to. At that point, ads or renting of information are meaningless... because it won't be used.
For a proximity-based application like this, purposely excluding the majority of smartphone users seems like it will be a limiting factor in its adoption.
But, who knows, maybe this is all intentional. I'll optimistically assume they are beta testing with iOS users until the kinks at worked out and can release to Android.