> So basically he has just transfered his communication tasks to another person and somehow it is ok for him to enslave a person for jobs he doesn't want to do since he's a much more "important" human being. This is pure arrogance.

You know that this is like, the basis of entire civilization? The specialization of labour - you do what you're good at, I do what I'm good at, and we exchange the value produced by our work. His secretary is probably being paid for the job, and given that he/she specializes in e-mail correspondence, he/she will be much more efficient with it than Knuth himself could ever be.