I'm not so sure, there's a world of difference between a constant cadence of say for example 85-90ish for the UK/EU 15.5mph limit and 110-120ish (US 20mph) if there's no different internal gearing... US riders must be bloody fit and do they ever pedal through the limit, and at what cadence?
At least on Shimano systems the chainring has always the same speed that the crank with the pedals (and so also your cadence), at least when you are turning the crank in forward direction and thus the free wheeling mechanism inside the motor is not active.
So there is
no internal gearing between the crank and the chainring on a Shimano motor, just the freewheeling mechanism.
All Shimano motors (does not matter if EU or US) are the same in this way.
This situation is different on e.g. some older Bosch (or maybe other vendors) drive units where there indeed is some internal motor gearing between crank and chainring and so crank and chainring are moving in different speeds.
So the speed of the bike in relation to the cadence at the crank on a Shimano based bike is always ONLY depending on the size of the chainring, the selected sprocket size of your rear cassette and for sure the rear wheel circumference!
The internal construction (including gearing) of the motor does not matter at all for your cadence.
Just check on any Shimano driven bike that the chainring is always going exactly in the same speed like your crank with pedals and your feet, just like on any "ordinary" bike.
So, there is definitely NO difference regarding this issue on Shimano drive units no matter if it is a US or an EU version.
If you don´t want to pedal with high cadence on a US based bike, then you have to mount a larger chainring.
However, maybe bikes delivered to the US market already will get delivered with such a larger chainring (or maybe even a smaller smallest sprocket on the rear cassette) which would make sense to avoid the annoying "sqirrel cage feeling" with (too) high cadence.
Just to add some calculations:
My EP801 driven bike has the following parameters:
wheel circumference: 2300mm (29")
smallest rear sprocket: 10 teeth
chainring size: 34 teeth
This configuration will result in a cadence of
85rpm when going
40kph, which is easily manageable with the 600W max. peak power and max. 85Nm of the EP801.
The calculation for this is quite easy: 40.000m / 2,3m / 60 / 3,4.
Unfortunately the bike frame is limiting me to use a larger chainring size.