Originally Posted by S-Dot
So basically as soon as it detects understeer, it diverts power (up to 100%) to the rear axle, and the resultant behaviour is thus quite similar to the RWD.
The marketing sources you cite are describing what the car does when the tires are actually slipping
on the pavement from too much power. This has nothing to do with the fundamental handling balance of the car; any car will exhibit understeer or oversteer if the limits if adhesion are exceeded on that end of the car.
Front wheel drive cars exhibit tremendous understeer as a fundamental handling characteristic, as well as torque steer upon throttle application. This does not mean the front wheels are spinning.
AWD cars exhibit precisely the same characteristics of a FWD car to the extent the front wheels are powering the car.
Also, keep in mind the front wheel slipping under power understeer being addressed by xDrive is directly caused by the xDrive system itself!
This form of understeer will never occur with RWD so there is nothing to "fix.".
This is yet another example of xDrive understeer.