Pattern is full:
I'm just going to toss in one other difference betwen the U.S. and the U.K. Possibly overlooked since this is a pro pilot forum.
The flight levels (Class A airspace) REQUIRE an IFR clearance (except for rare SVFR). In the U.S. there are still a fair number of well-off private pilots who like to hop in their turbocharged whatsis, strap on the nasal oxygen, and fly VFR in the 'teens - without having to get involved with ATC over the wide open spaces (except towers, or the high-volume big-city airports with Class B protection.)
The average procotologist in a P210N flying from the L.A. basin to Aspen or Lake Tahoe would consider it "unwarranted government interference" to have to file IFR to cruise at 17,500' on a clear day (let alone 7,000' or lower). And they have a lobbying group - the Aircraft Owners & Pilots Association (AOPA).
Point taken. But, the turbocharged crowd is declining. The fat cats that fly their own high end birds are mostly turbo-props these days, and they come right on up into Class A, RVSM and all. Then, many of the turbo-chared that are around today can, and do, go as high as FL 250.
Then, there is the Cessna Mustang Mach 0.61 single-pilot jet that can go to FL 410. If they go to 410 they aren't such a problem, but at FL 350, or so, they clog the system as bad as King Airs do.