Note that Knuth has written dozens of books and is perpetually making edits and corrections to them (not just typos, but often extensive rewrites while making sure that the book remains coherent as a whole): this is an activity that comes easily to him, so one can see how he can do it with programs too. The rest of us may find it harder.

But then again, we can ask: if we cannot keep the program's document structure as a whole up-to-date, then are we really editing the program properly? A major risk of introducing bugs is that one may edit a part of a program without taking into account the broader context, such that the integrity of the program is lost, and literate programming (which forces us to update "the whole program" every time) can be considered a mitigation of this risk… so IMO the greater time that it takes to update the whole program could actually be a good thing, saving time in debugging or whatever.

Edit: Also, part of the trick is to put only as much as you think is really relevant in the "text" part: literate programming does not necessarily mean over-commenting everything (Knuth doesn't either), it's just an orientation that what you're doing is writing a document. It's ok for most of that document to be code, as long as you think you've presented it well enough.