The UK ones (and yeah somehow there are UK ones) like to distinguish between a car and an mechanical horse. Of course a car is an mechanical horse but in their minds there is a distinction.

I think a lot of it stems from the fact that when cars first came into existence no one really quite knew how to define them, so they were often just classified as horses. For the most part this worked because back then most cars could barely go above 5 miles an hour, so there wasn't really any reason to have special laws.

Of course laws have been updated since then, but let's not take that into account.