Comment by dhosek

I think some of it is just aligning with more modern computing technologies combined with the people who write the materials have lived rapid evolution of computing technology and decided it was best to use a generic abstraction that better reflects contemporary technology. I’d note that Knuth, in The Art of Computer Programming moved his abstract machine from MIX to MMIX, the latter being a RISC instruction set, the former being more aligned with 60s style machine instructions.