Surely parking the really big ones must be a problem in some multistory car parks, in the UK at least...

You won't see any of the really big SUVs in the UK (except the odd HumVee that some nutter has imported). In the US (Seattle at least), every sixth car on the road is larger than a BMW X5 or a Range Rover. It's hard to believe how big they are until you see them next to a "normal" size car.

Parking spaces in the US are bigger that in the UK as well and they have spaces marked as "compact" which are about as big as the ones here.