I don't see how you can allow lowercase "m" and "u" as symmetrical without also by the same principles including "n." In which case there are other words like "nun" and "non." Also "MAM" and "MOM" are symmetrical and are words (at least, Scrabble words. He only includes "MAAM" which oddly enough is not a Scrabble word.)
> He only includes "MAAM" which oddly enough is not a Scrabble word.
What's odd about that? ISNT, DONT, ARENT, COULDNT, SHOULDNT, none of them are Scrabble words. More generally, you're not allowed to misspell words in Scrabble.
More along those lines here: http://www.fun-with-words.com/word_records.html