oil pump question ?

Those are not fixed flow restrictions like being referenced; the are physically designed quite differently. And flow restrictors do have some variation in flow with pressure; approx the square root of the pressure difference. Here is a calculator:

http://www.tlv.com/global/TI/calculator/water-flow-rate-through-orifice.html

Do the bearings in an engine behave like a fire hose or a flow restrictor? That I don't know, but the flow area is not shaped anything like a fire nozzle.

Edit to add: And actually a fire nozzle works to increase velocity of the flow with its tapered design; it is not designed as a flow restriction per se. I assume it is the same for a water jet; the velocity increase will result in the energy of the water particles increasing by the square of the velocity change. 10x velocity change ==> 100x water particle energy. So, the jet cuts and the fire nozzle directs water many stories upwards. I can't see any analogous part in an engine oiling system discussion.......