I don't think knuth does modern TCS stuff, the "old guard" (80s-ish) was focused on either classical algorithms / combinatorics, or the start of systems programming (db, network, os). Yes, Knuth did quite a bit of math in TAOCP, but they're very much "old" techniques.

Modern TCS is about unifying a lot of the ad-hoc approaches of old, as well as analyzing different models of computation that better model reality (EMM, streaming, distributed, etc).

I like both.