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I assumed there was some relation between k T log 2 joules and 20 Watts, probably giving some sort of context to how easily or not easily information in our brains could be lost. The theoretical principles behind the amount of energy required to erase one bit, while interesting, doesn't necessary matter for that relationship, does it?

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Landauer's principle would come into effect if you had a theoretical "Computorium" material that could perfectly turn energy into computation. Then the computation you could produce per volume of space would be limited by it.

Our brains are (very) far from being the perfect computing material (so are our chips).

The theoretical minimum is only useful here to show that our brains cannot do free work. (Irreversible) computation always has a cost.

The 20 Watts are the important number. Our brains have a certain energy budget and have to perform within that constrain.

the log 2 comes from Shannon coding, because information (tm) encoding is modeled on a bit string of discrete energetic states (something quantum, too, I guess). And there is a transformation to the frequency domain (ie via discrete fourier transform). Entropy is always messured in Watt, doesn't. make sense to equate psychologic information content with physiologic enthropic consumption.

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