I think it mainly comes down to supporting the app long term. Iphone apps are painless because you already know the device types and usually only have to update them when the OS gets a major update.
Then if you look at the Android phones you've got countless companies making phones of all different sizes, speeds and quality. It gets pretty ugly trying to validate things work on all the devices.
It really doesn't matter what size/speed/quality a phone is. You simply design it for the version(s) of android you want to support. Using that argument would be like saying it is hard to make a windows app because of all the different types of windows machines out there. Nobody builds an app with a specific machine in mind - they build it with a specific OS in mind.
For example, the latest version of Android is marshmallow. If you make an app that works with marshmallow, then it will work on every phone that has marshmallow. It's that simple. And it is the same on the iOS side.
Your also forgetting that there are different sizes and capabilities in the apple ecosystem as well. The 6, 6s, 5, 5s,etc....
My point earlier though is in regards to apps that really should be able to run on *anything* based on their simplicity.
2 years ago Little Mermaid came back to theaters and we decided to take our daughter as her first movie. She was 3 at the time. They heavily advertised an app that would allow the lyrics to show up to all the songs, answer questions about the movie, etc... As in, there were actually segments in the movie where things paused so the audience could interact on their device. The problem was, it was for Ipads only. Not Iphones. Ipads. Considering I own a pile of kindles and yet another pile of android based tablets, it was frustrating to realize I had nothing that was compatible with this app. And there was no reason not to port it. We aren't talking some technical achievement here. We are talking about a very basic app that just displays lyrics, facts, and a few other things during a movie. Not only should it have supported other tablets, it should have supported iphones and android phones as well. Otherwise, why integrate something like that into a theater showing to the point that it is disruptive for every family in the audience that doesn't own an iPad. Anyways, sorry to derail, I just see a trend with them when it comes to their companion apps that tends to be frustrating.
In this case, I can thank them I suppose for making it real easy for me to turn down their $200 box of ghost leftovers.
