By the way, just how much class G is available up to FL195 in the USA?
Not much. Most of the USA is class E. Free flight VFR, IFR with no en-route charges. Mostly covered with WAAS and precision GPS approaches to GA airports, even ones without towers or radar coverage. Radar service and flight following with no en-route charges. Pop-up IFR clearances available at most places. No class A below FL 180. VFR transits through class B in most places. Other than that, it's just like the UK.