Good point. I really don't know how to explain it now.

I have read articles about NHTSA making some tire pressure measurement system standard (after the Ford/Firestone debacle) and the two systems that have been proposed are: 1) pressure transducers that transmit pressure via radio signal and 2) use of ABS wheel speed sensors

The car companies like 2) because it requires the least amount of new hardware (cheaper) but it won't work in situations I described above, where all 4 tires are deflated the same amount.

Like I said, I can't explain it, but apparently it works, somehow.