Does anyone have any first-hand knowledge of somebody actually being charged the $20?
As others have pointed out, I would think this could be a very difficult policy to actually follow through on, given that a guest is given no "proof of cancellation", and that apparently the gremlins do get into the reservation system and cause errors.
This isn't like a single restaurant that handles all of its own reservations, though even they would have some issues actually administering the policy.
WDW is going to have more no shows just due to the nature of the entertainment offerings all around. Maybe your plan was to spend the day at BB, go back to the hotel, change and go eat at CG, then go to MK for Spectro and Wishes tomorrow. But it rained all day, or BB was closed due to lightning, so you decided to go to MK that day instead to catch Spectro and Wishes. Or the baby was ill and you decided it would be best for everybody to stay in the hotel room.
There are plenty of perfectly reasonable reasons to call CG and cancel your ADR for that night, yet they're going to charge you $20 because you didn't call early enough?
C'mon. I'm as cynical as just about anybody with respect to how Disney has changed the way it operates and services guests, but I can't buy into them really following through on this.
Then when you figure that saying you cancelled turns into a "he said, she said" thing no matter when you called, I really can't see them pushing this.
Not that I agree with it, but my best guess is that just the threat of the charge is being used as a deterrent.
As for paying extra for specific viewing locations for things like Illuminations and Wishes, its not as simple as saying "Disney is a business and some want to pay, so why not charge?"
Clearly, there are valid business reasons for not charging as evidenced by those guests who don't like the idea, and by the fact that, for the most part, Disney has not adopted this policy. Even with Fantasmic, the dinner package guests are not given the "prime" locations.
I'm sure Disney has been tempted to implement something like this in many more areas than they already do. At the same time, even my cynical side says they also realize there are significant drawbacks to doing something like this. (Certainly they haven't refrained just because they haven't thought of it...)
They have to balance what may seem logically or economically "fair" with the practical implications it has on their overall business.