Level 4 cars need a steering wheel to be generally useful. But a limited vehicle like a taxi doesn't need a wheel, no matter whether it's 4 or 5.
I agree with the rest of what you said. Geofencing entire continents isn't about driving ability, and blizzards are an acceptable human-level restriction.
However it looks like this just changed: https://www.nhtsa.gov/sites/nhtsa.gov/files/2022-03/Final-Ru...
“For vehicles designed to be solely operated by an ADS, manually operated driving controls are logically unnecessary.29 To account for this, the NPRM proposed a regulatory scheme in which the affected standards would not assume that a vehicle will always have a driver’s seat, a steering wheel and accompanying steering column, or just one front outboard passenger seating position.”
They are apparently allowing level 4 Taxi to be considered full ADS even if they have additional “Stowed controls” options.
https://unece.org/DAM/trans/doc/2013/wp29grsp/WP.29-161-18e....
Geofencing is part of the criteria, but a car that can only drive in the USA but can’t drive in Europe still qualifies as level 5.
Similarly a car that refuses to drive in a blizzard but can do everything else is level 5. Being able to drive at night or moderate rain is mandatory however.
That said, there is plenty of slightly different definitions thrown about. I am sure someone is going to argue a car needs to be able to drive in any country to qualify etc etc.