Sure, but (based on anecdotal experience of places I know along the Thames) there are lots of places where houses are built to expect at least some level of flo

Sure, but (based on anecdotal experience of places I know along the Thames) there are lots of places where houses are built to expect at least some level of flooding - steps up to the door, etc. - meanwhile cars left on the street can go very quickly (e.g. overnight) from fine and dry to completely screwed.