The Devil is definitely NOT in his details.
I heavily disagree with his evidence he uses; he points out problems with the code of the game (such as monster AI's attacking the wrong opponents) and calls that a failure of the d20 system; he goes on to say that monsters are "cookie-cutter" under d20, and this somehow causes problems. What he's instead pointing out is that previous versions handled mechanics not directly relating to combat with a minimalist approach; it's a valid way to play, but it means that earlier game designers were free to ignore or invent rules, for everything from NPC interaction to swimming, on the fly instead of having to properly code them by a standardized set of rules.
Cookie cutter monsters? The system that has
Half-fiend axiomatic insectile minotaurs of Legend? That may be templated, but that's one funky-looking cookie.
In short, he's complaining that d20 rules are not good for computer games because they aren't systematic enough, but then goes on to quote examples that show that it's so systematic that it's hard to implement them?!?!
If anything, the earlier designers on games like the SSI gold box games used to frequently say back then that they wished that the AD&D rules had been MORE systematic at that time, and not as arbitrary as they used to be (the STR bonus scales, THACO, surprise, thief skills vs. other skills, etc.)