While that is true, I look at it this way:
An n/a car at the beach at WOT might have a MAP at 100 kPa, so the when it wants to see how much fuel to inject it goes to the 100 kPa cell and the rpm and looks up that value.
Same n/a car in the mountains at WOT might have a MAP around 90 kPa, so the when it wants to see how much fuel to inject it goes to the 90 kPa cell and the rpm and looks up that value instead.
Or interpolates between the applicable cells to get those values, but you get the point.
And the same thing happens on a turbo car, 20 psi boost will have a different MAP at the beach than it will in the mountains.
Now if the cells at 100 kPa were dialed in pretty good but the ones at 90 kPa were not, then there is some tuning to do. But the fact remains that the system recognizes automatically that the air pressure is lower and will start looking in different cells to get different fueling. The amount of tuning will depend on how well those cells were dialed in before.
John