RC,
I agree that if you are a "dumb amateur" you should not mess with the tire pressures and just use factory recom presures for the street which are meant to work on avberage for the whole world and optimised for tire even thread wear and durability.
However you will find very few experienced drivers with factory pressures on the street. With a minimum experience and sensibility you can easily notice improvement in grip and handling from varying a just a few PSI's of the tire pressure according to the weather in your region or season (mediterranen summer day vs english winter day), style of driving (hard vs cruiser), average speeds or type of use (city or commute vs canyon or highway), and espicially tire brand and model (long lasting confort tire vs hard shell performance tire), which are so different amongst them that pressures are not universal. The PS2's are the ones that I found that run closest to the factory recom pressures BTW.
So they are not lowered (slightly) on the street for the same reasons than for the track, on the track you lower them much more than on the street because they heat up so much more that your running hot pressures would be excessive otherwise. So on the track you should worry directly about the hot air pressures anyway, the famous 40psi ballpark, the variabililty is so much bigger than in the street as you say.