Another Grammatical Oddity

Watching an American TV programme this afternoon, I was struck by an expression used in the USA, viz "I could care less", when what is meant is "I could NOT care less". Why is this ?

There's another one too which I have noticed a lot of late, to do with stressing a particular word. Americans say - and the capital letters indicate the stress - "It's not your FAULT". This indicates that it may not be your fault but it is your something else, whereas what they really mean is "It's not YOUR fault", ie it's someone else's.

Two countries separated by a common language !