Why do dogs w/ white coats become prone to Deafness?

It’s not necessarily a cause-and-effect correlation. Just turns out mathematically enough that people are making such generalizations.

White blue eyed cats are prone to deafness geneticly. I never heard of this in dogs

There’s a connection between hereditary deafness and a gene for coat color. Predominantly white dogs as well as merles are affected. The highest incidence is in dalmations but there are dozens of breeds affected.

If you want detailed info -

This is actually a misconception.The color of the coat (white) has nothing to do with the hearing. I have a miniature Australian Shep hard that is mostly white and while looking up some things on them I read that they were called lethal whites.(http://www.lethalwhites.com/lethalwhite.html) What happens is when the ear hair (you cant see these fine hair) has no pigmentation (white) then the dog tends to be deaf or hard of hearing. However they do tend to make up for the lack of hearing in other ways and alot of the time you really cant tell unless they are totally deaf. My dog is mostly white a double Merle Aussie and has no hearing problem, so I don’t think this is the norm just the exception.