Calvin and Hobbes has killer vocabulary too!

Reading is a skill as well as an intellectual pursuit, and require certain muscle groups to work together properly. Scanning the page with fluency is just as important to reading as knowing which letters make which sounds. Eye muscles have to be developed to a certain point for this to happen; otherwise, the eye loses its place and the mind loses the thought, and reading becomes a frustrating activity. This is also why so many children's books have BIG LETTERS and lots of friendly, restful white space on the page. Practice in small bits of text with big letters, then bigger bits of text with smaller letters, then regular books.

Little details like this lead people who study reading to suggest that there is a minimum and an optimum time to teach it. It's not supposed to be an age rule cast in stone, like the drinking age.

The parents of the family you mention apparently took that "magic" number of 8 to mean that 8 years old is when literacy exposure should start, which is a biiiiig mistake. Children model behaviors they see, and they associate activities tied to closeness and comfort with pleasure. Reading aloud even to babies is vital to this feeling.

Not only that, but the vocabulary that a young child can understand and use is usually several levels above the vocabulary a child can read even in the most literate household. Exposure to books above the child's reading level as part of read-aloud time will build that vocabulary and make the child a better decoder of unfamiliar words later. If you've heard it before, it's easier to figure it out on the page, using phonics and context together.

Those kids might turn it around for themselves, but I'm afraid they're more or less on their own.