It's an interesting question, I drove around for years without worrying too much about it. If the OIL light isn't illuminated, must be OK, right? And that's true so far as that goes, but an otherwise good engine can be turned into more or less scrap with loss of oil pressure in just a few seconds.
The pressure specs in the manual are listed for recommended oil viscosities I expect. And from what I've gleaned from reading the material is that a high oil pressure is not necessarily "good" simply for high oil pressure sake. For example if someone were to run 20w-50 and saw 70 psi HOT at idle, that isn't really what we want. The bearing clearances are kind of what's important here, and excessively high oil pressures means the oil pump can go into bypass.
If the engine is in good condition, it should achieve the specified pressure with the factory 10w-30, one of the most important functions of motor oil (other than actual lubrication) is carrying away excess engine heat away from internal engine components that aren't very well served by the engine cooling system. For that, the engine needs good oil flow, and plenty of it. I think sometimes when it comes to motor oil a lot of us try to out think the engineers.
