This keeps grandma from accidentally stumbling onto something offensive by mistyping one character.

For example, they stop autocompleting on the word cuckoLd at the letter "L". That happens to be the point at which it diverges from the word cuckoo. I know I wouldn't want to be searching for a cuckoo clock, mistype one letter, and suddenly have a bunch of stuff about adultery on my screen (or worse, a bunch of x-rated images).

This was probably obsoleted by Safe Search.