Why Did Natural 20's Become Automatic Hits?

Here's an observation I just made, that came up from a friend's question about the 1E AD&D rules for a big project they're working on. Ultimately this highlights the less-than-optimal state of editing in those books. You may know that 1E AD&D did not have a "natural 20 always hits" rule, but it did show a repeating sequence of 20's in the to-hit tables (DMG p. 74-75): A few pages later, there's a…