We have seen this in the newer Bosch ECU's. In the old days you hand closed loop running and open loop at WOT, with fueling at timing maps for each.

Now, with the closed loop operation at all times, in some applications there is what we call a Lambda map as well. You can go in and change the fueling maps and the car will still run to a certain lambda value if the lambda tables are not changed as well. There are literally dozens of maps in these ECU's that can be massaged to adjust the fueling/timing/spool/peak boost/boost curve/etc.

Essentially what is occurring is the ECU is pulling fuel to the target values in the lambda map, within certain limits.

As you have said, each car and application is very different. Some like running at different lambda values than others.