More likely that the owners don't want to get their pretty and pretty expensive toy scratched than any problems with the capabilities of the vehicle.
Yanks certainly do take them off road into very harsh conditions. In the snow belt they get hard use all winter. In my last three trips to the USA I saw one real Land Rover, a Series III 88" in Reno. There are Range Rovers aplenty as they are sold into the city luxury market. Land Rovers are not highly thought of there being regarded as too small, too slow, underpowered, too low for the snow belt and like Australia, too few dealers and almost no back
up.
For those not familiar with the ex-urban areas in the snow states, just about everybody has a big pickup with high clearance, huge tyres just for getting into town when the roads have not yet been ploughed. Low vehicles will belly out on the snow. Many folk have a "winter car" usually a big old yank sedan or wagon that can rust out from the road salt and slide into snow banks on icy roads whilst the good car stays home in the garage.

