I think it's pretty widely accepted that the majority of people who buy cars do not modify them. Most people leave the cars stock and those who do modify are definitely in the minority (not majority).Well, if Ford is smart and accepts their customers (a majority of them especially the ones that buy performance vehicles) will want to modify them in some sort of way! Therefore, Ford needs to continue and grow / add more products to their Ford Performance line! A lot of manufacturers have gone this route - some German ones have a full blown OEM aftermarket tunes & products for their customers. Plus, what a great way to capture even more revenue from this market!
But the people can be broken down into even smaller groups to analyze. Lets look at the SHO, it's a pretty small market to start with and nearly everyone leaves theirs stock. There just isn't much market for Ford to develop a new factory tune for the SHO when there isn't much market. But if you compare that to something like the Mustang, even a small percentage of total sales amounts to a large number of people who tune their cars. As a result, Ford has seen there's a market and they have started developing options....http://jalopnik.com/fords-warranty-preserving-ecoboost-mustang-tune-is-fina-1787660757
The problem with the SHO is that it will never be as big as the Mustang and have a pretty small market for much aftermarket. If the SHO motor was ever completely different and locked out, it's likely nearly all tuners would disappear. It wouldn't be worth it for them to go through the R&D for the small SHO market. But since it is shared across platforms, that R&D can be spread across multiple platforms to make a larger market.