You are correct. Only “some” 737 NG’s have dedicated AOA displays. I am sincerely trying to avoid A versus B and just present facts.
However, any 737 NG with a HUD has, for all practical purposes, inertial AOA displayed.
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True, it is a customer option.
The concept of having safety enabling features as "customer option" is somewhat scary. Assume an accident happen and the accident investigation finds out that "lack of AOA information to pilots contributed significantly to the cause". Should the blame fall into the airline beancounters who saved by skipping an "unnecessary option". Or the airplane maker, whose business model includes making extra profit with optional features?
To get back to AF447, the Air France beancounters were reluctant to upgrade pitot tubes to safer ones. I have no idea what the price of the pitot upgrade was, but probably it was not cheap, since it got beancounters on their toes. Blame beancounters? Well, the other side of the coin is that Airbus/Thales was making a profit on what was essentially a safety fix...