The sad fact is that we're now back to the situation in the 80s when we had about a dozen utterly incompatible platforms with different processors, operating systems, interfaces, admirers, haters - the whole "my thingy is better than your thingy" scenario.
In an age when we can ride virtual horses though wonderful landscapes we are now reduced to retro 2D games running on mobile phones of various shapes and sizes. In theory this should be easy, but what we're seeing is a rats' nest of incompatible flashy rubbish consumer devices that don't multi-task.
None of the manufacturers want cross-platform development. They want killer apps that will sell their units. There never will be a simple answer to this - there will be new phone-like gadgets coming out of Korea or probably China with another new system. We're back to chaos, and we have to get used to it.
As I said before - develop your game and make it great. If necessary pay somebody else to complete the final stages of the port. If you started from scratch learning all the compiler operations and SDKs for all these platforms you'd either go mad or be working for TGC (or both!).
Accepting the 99.9% figure, there are about 6 million people who can manage the job. That should be enough.