They do it to prevent customers returning for oil pressure gauge issues..."it takes too long to get oil pressure" and "the oil pressure fluctuates a lot"; if you manipulate the gauge so that it behaves the same every time, no issues.

The actions of the gauge are based solely on the ECM...the oil pressure is sensed by an on/off switch set at 7psi. While it is close to actual, on start up; its not even close.

i wonder if any one has taken a mechanical and showed the difference?

Yes, I have one on my dash...