I haven't seen the older editions, but aren't they also
beautifully typeset? (I thought he wrote TeX so that
he could present things the way he wanted to in these
books.)
Comment on RE: RE: Knuth books and programming (kudra: TeX is beautiful)
Yes, that's the reason he started writing TeX. But I think the
older editions were not typeset with TeX yet. I have the
impression I read somewhere that he gave his original books,
together with all his corrections, for someone to typeset
in TeX for the new editions. I could be wrong.