There's material in the 2nd ed. that's not in the 3rd ed. and vice versa as I understand it, so having both might actually be a good idea.
Hopefully the stuff they removed was the stuff that's no longer relevant/useful in the 21st century. The "digital" section has a lot of stuff that's hopelessly outdated, eg. the section on assembly language using the 808618 instruction set.
And does anybody still mess around with flip-flops now we have ubiquitous microcontrollers...?
What the hell! Me!
I'm studying a two year electronics course at a vocational training school. We learn and mount circuits using. combinational and secuential circuits all the time on "microprogramable electronics" subject, soon we will learn to develop for Arduino too.
Despite it might look outdated, many teachers believe this classic style has a more didactic value to learn the grounds of basic knowledge, they are still used for easy circuits and many systems use software to do visual programming using them as abstraction (such as PLCs).
I disagree about removing them. I would make AoE all digital and live like with Oxford and Cambridge dictionaries. This way it can have no page limits and constantly updated. Paper versions would be like a selection of the most relevant parts of it. Some parts could have historical relevance, even for making replacements of old circuits.
For an example of what happens when an author follows the continuous update route, look at Don Knuth and The Art of Computer Programming. Volume 1 was published in 1968 - 47 years ago. Planned to be 7 volumes, but to date, due to revision of already published volumes, we have Vol 1, 3rd ed, Vol 2, 3rd ed, Vol 3, 2nd ed and Vol 4 being published in a series of fascicles, 5 currently published, I believe.
Dr. Knuth is 77 years old or so, and hence it's extremely unlikely that the projected 7 volume series will be completed.
The Oxford dictionary staff is >> two people, and it's practical for them to publish a dictionary over an extended time, with annual updates. And, after all, the first edition of the OED required 40 years (1888-1928) to publish the original 12 volumes. While later editions have been published on a somewhat faster cycle, it's still a slow process.