Heinz, I agree with what you say about manufacturers playing safe.
I had a Ford Focus turbo diesel. It came with two engine options of 90 or 110 ps.Before buying I did some research and a test drive. As far as I could find the only difference was in the mapping. No indication of other modifications. Even tne salesman (Ford) was non committal.
Manufacturers will simplify things to make it easier for production (less variation to deal within the factory), and also a safety margin to keep engine components well within limits of strength.
If you tune an engine then there is a small range available within design limits bevore you need to replace components with stronger ones. Knowing the limits is very important!
