I've found a suspiciously high percentage of the people who have totally! read the Art of Computer Programming are unable to answer even basic questions about MIX, by the way.
Reading can just mean reading word by word, symbol by symbol then putting the book on the shelf. That ends up happening a lot with material that has a lot of formulas and theorems. It could take days for some to understand just a couple of pages.
So basically I not surprised at all that you've met so many people who've read the volumes, but didn't all the subtleties.
I think reading the volumes is the next step in status show-off step after buying and putting them on the shelf.
Also, as many have pointed that MIX is just too obscure. Not knowing much about doesn't really indicate a lack of theoretical knowledge. I would personally skipped over those chapters.
I've seen several equally dense, informative CS books (such as Dick Grune's _Parsing Techniques: A Practical Guide_), but Knuth has a specific sort of cachet among xkcd-quoting geek hipsters, so people namedropping him, make a pretense of having read them all the way through, etc.
(Knuth denies this ever happened.)