Right, and as I explained at https://news.ycombinator.com/item?id=20488446, if you have negated versions of all the literals available, you can make not just XOR but any arbitrary Boolean function as a sum of products (or a product of sums, CNF), just like a PLD does.
"Luxurious"? I'm not sure what you intend to say. Do you perhaps mean "unnecessary" or "essential" or "very strong" or "very weak" or "well-thought-out"?
As I read it, he's pointing out that since the diodes and resistors can't do things like XOR, because it's not monotonic, it's necessary for "[e]ach input variable" to be "presented in duplicate".
Another example that is in some sense more fundamental than XOR is the MUX function b if a else c. If at some point b = 0 and c = 1, the output is the negation of A, which diodes and resistors alone cannot achieve.
"Luxurious" is a term from psychology, where it's used to describe "ornamental" behavior, which may be hinting at something deeper. ;-)
In the particular case, I just found it interesting, since the duplicate outputs are already well established, before the text "withdraws" to monotonic functions (for which both inputs are used). A bit of an understatement.
Edit: I think, "luxurious" as used this way is a great term, because it doesn't attempt to apply any classification. It's just pointing out that there's a somewhat independent process, which consumes energy.
