Usage does change throughout the decades. Usage would change the meaning of any given word. For example, the word GAY used to mean light hearted and carefree. Now that word has become a term. It is a term used instead of the word homosexual.
When the CNN/HLN host said, I couldn't hardly care less, she was speaking incorrectly, grammatically. The correct way is to say "I could hardly care less." The term hardly is the negative word that replaces not.