Are all white cats with blue eyes deaf or just hard headed?

First thing is first, not all white kittens are deaf. It is usually ones with blue eyes.

Second, it is to do with genetics. There are certain traits in a creature's DNA that make up what they look like, how they act, what diseases they will have, and basically anything. Have you heard of dominate and recessive traits? A white kitten with blue eyes all have dominate traits in their DNA that cause them to most likely be deaf.