There are a few threads around that addresses this in detail. The short answer is that pressurized storage makes it much easier to attain and maintain stratification, avoids the cost and heat transfer loss (delta T) of a heat exchanger, and eliminates evaporative loss. Because there's no need to ever access the tank, it can be insulated more completely.
The improved stratification and heat transfer means that you get more effective storage with a smaller tank.
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I will give you that pressurized storage can be operated at somewhat higher temperatures.
I would question whether stratification is any better. Heat transfer might not be 100% with a hx but this is not lost energy, it might require a circulator to operate to a few minutes more to compensate.
Evaporative loss is an issue if you do not seal a tank properly. An unpressurized tank with a cover that is easily removed allows simple retrofitting of solar or other hardware heat exchangers and modular service if ever required.
A well designed unpressurized tank will perform quite well. Yes, you need heat exchangers (sometimes), but you usually use one somewhere with a pressure system for DHW.
Yes, they are not as cheap as a used gas tank, but if you are a professional installer and actually have to bill for the time to get a pressure tank into a building (or build something around it) and tie multiple tanks together with black iron pipe or even big PEX and insulate it with spray foam, I think an honest tally would be closer than one might want to think.
Unpressurized tanks are not for every installation, but they perform with excellent stratification and can usually go in anywhere. We can get a tank into a basement through a 25" square opening--for tank and heat exchangers. All in about ten minutes, usually without swearing or damage to stairs, walls or people.
I think where most people feel the need for pressure systems is with big heat load installations that cannot tolerate a very large temperature swing in really cold weather.
More moderate heat loads and better designed systems work beautifully with non-pressurized storage.
Any storage is better than none!