> If Computer Architecture were a really healthy field, classes would have to be taught from recently-published papers, because it was moving faster than a textbook could be published.

I really don't get this perspective. How can you possibly hope to understand "recently-published papers" without first understanding the basics of the field, which is what Hennessy and Patterson covers? Every subject has introductory textbooks from which introductory courses are taught, and then you can take more advanced courses that can, among other things, include material from recently-published papers. Are there even any fields where courses must be taught from recently-published papers?

On another note, it's not like no more computer architecture textbooks are made. Look at the Synthesis Lectures on Computer Architecture series.