I've wondered about this for sometime, and I'd love a good discussion on it. Now I know there are certain issues that will vary by market, such as;
1) necessary LTE frequencies
2) default language
3) government certifications
4) regional hardware customs, like dual SIMs
5) distribution channels
But I can't help but wonder if the falling cost of hardware, storage, and globalization of distribution channels (Amazon), has made a lot of these issues easier to address without creating a boatload of different regional and carrier variants. Just include features and frequencies that may not be absolutely necessary in every market. It's probably cheaper than creating so many different versions. I look at the wonderful array of Nokia models available globally, and then just get frustrated with how only a couple of the lower line models have the North American frequencies. Why can't we make more true "world phones"? To me, it sure seems like that is the way of future.