Not actually true - the first ever "hatchback", the 1938 Citroën 11CV Commerciale had a ~65° rear opening:
In some English speaking regions the rather stupid and arbitrary "liftback" distinction was never widely accepted into popular language, they are calling them all hatchbacks.
For example if you look for the "top 10 hatchbacks" on UK websites, you will get 10 cars with very non-vertical rear openings:
Not
one of these 10 hatchbacks has a "near vertical opening after flow detachment" I believe.
Again, let's please not get hung up over "hatchback" versus "liftback" semantics, I think you knew exactly what I meant, and you pointlessly derailed the argument into interesting but even more off topic directions.
No. When people were talking about hatchbacks the other day, and I said that I think it's unlikely Tesla would do a hatchback soon (more likely later as battery prices drop and energy and power densities rise), my interpretation was precisely of hatchbacks. Not liftbacks. When people refer to a hatchback, they generally refer to a vehicle with a steep rear hatch. Even your example of the 1938 Citroën 11CV has a steep rear hatch, so I'm not sure what you were trying to show by bringing it up.
Until I get my Model 3, I'm still stuck driving my Gen1 Honda Insight, a liftback. I've never in the entire time I've owned it heard anyone refer to it as a hatchback.
Here's the rear ends of the vehicles in your linked article:
Ford Focus: steep, after flow separation
Volkswagen Golf: steep, after flow separation:
Seat Leon: Steep, after flow separation
BMW 1-Series: Steep, after flow separation:
Mazda 3: Steep, after flow separation:
Kia Ceed: Steep, after flow separation:
Honda Civic Hatchback: Probably the least steep of the bunch, but still too steep, e.g. post flow-separation.
Audi A3 Sportback: Steep, after flow separation
Mercedes A-Class: Steep, after flow separation
Vauxhall Astra: Steep, after flow separation:
Not one of them is a liftback.