Truth and Knuth is an author of books so it makes sense for him to write code for books when writing code for books. However code that isn't bound into book has different needs and should be different. I've printed out code before (the floor gives a lot more space to spread out text than even the largest monitor, and taking a pen to circle useful parts is helpful) - but I recycled that paper as soon as the bug was found/fixed. In that case I'm never interested in how the code is documented/supposed to work in the authors imagination - I care about what it actually does.