If you want your App Brand to dominate in a specific niche in the mobile world, you have to publish apps on all mobile platforms.
That way, your App Brand will be agnostic to the mobile devices your customers might have.
It will become extremely effective to advertise your apps simply as a mobile brand offering a specific service WITHOUT paying attention to the end-user mobile devices.
Once you decide to go cross-platform, here is a list of App Developer Accounts you will need to create:
• Apple Developer Account
Cost: $100 per year
• Google Play Developer Account
Cost: $25 one-time
• Amazon App Developer Account
• Windows Phone 8 Developer Account
Cost: $19 per year
I do not include Blackberry in this list because that platform is not growing at the moment. I, personally, prefer only publishing on growing mobile platforms.
That is, besides $25 one-time fee, your overall yearly cost of having App Developer Accounts on all growing mobile platforms is only $119!
In my view, this is simply amazing!
To Your Success!