There seems to be confusion regarding the term OAT (organic acid technology) vs HOAT (hybrid organic technology) vs IAT (inorganic acid technology). Neither of these terms have anything to do with the ethylene glycol, the main component of antifreeze.
Coolant and the Acid Problem (nothing to do with OAT/HOAT/IAT)
Coolant heats up and cools, and slowly mixes with oxygen from the air over several years. Keeping a sealed system slows this process down a lot, but oxygen will still enter the system through the expansion tank. The oxygen from the air will slowly react with the ethylene glycol to form acids. The acids will erode the metals, especially aluminum. Acids and heat will slowly break down nylon, a problem if you have coolant going through intake manifolds. In fact, ethylene glycol, itself, is an organic compound. (Don't confuse the common term organic as used in the food industry.... a completely different use, and misleading when it comes to chemical discussions)
Solution to the Acid Problem: Buffers
To prevent the erosion of the metals, you must prevent the oxidation of ethylene glycol. This is where a chemical mixture called a buffer comes in. All antifreeze contain buffers. They protect the antifreeze from going acidic by neutralizing any acids that do form. After a number of years, depending on how well maintained the cooling system is, the buffer will get used up and no longer be able to protect the coolant from going acidic. Pre-1990 coolants used silicate based buffers (inorganic based), but those buffers got used up after just a couple of years so they looked at trying different buffers to get long life coolants.
What GM Did: Dexcool (OAT Buffer)
GM developed Dexcool which uses 2-EHA for its buffer and is organic based (based on carbon). This works well, except is very acidic when it gets used up. As long as you keep your cooling system maintained, and change it at the recommended intervals, it should be fine. The problem is you cannot see when it goes acidic. If you have a faulty radiator cap, or a leak that introduces more air than it should, you can easily use up the buffer before the 5 years and the acids and heat will eat up any aluminum and nylon rapidly.
What the Others Did (HOAT Buffers)
Other manufactors developed a hybrid organic buffer which contain an organic (carbon based) with low amounts of the traditional silicate buffers. G-05 uses benzoate (organic) with silicates (inorganic).
One could write an entire textbook on cooling systems. The chemistry behind them is very complex, and I've tried to simplify it for the general forum. The main purpose for doing this was to dispel the idea that ethylene glycol is IAT and propylene glycol is OAT. This is completely false. In fact, both ethylene and propylene glycol are organic because they're based on carbon. In chemistry, organic simply means the chemicals are based on carbon. The old silicate based buffers had not carbon in them.
In the food industry, the term organic is used to mean grown using natural means. There are a whole pile of regulations related to organically grown, but all plants need carbon dioxide (organic), and also need nitrogen (inorganic) and phosphate (inorganic)! Worse yet, organically grown means grown without artificially made pesticides/herbicides etc, which themselves are often organically based from a chemical point of view.
