General but technical question re: oil pressure guages?

[Orkrist2]

So, why is it that my MB and my MG have "real" oil pressure gauges, meaning they provide a real time oil pressure reading while driving and it fluctuates. Then, more modern, particularly US cars, seem to have oil pressure gauges that just go to a certain point and stay there, and at least are always in the "N" zone, which is pretty much the whole gauge, rendering them useless unless the damage is likely already done. Can anyne explain the difference ion how thse work, and how the "US" gauges can still be called oil pressure gauges?