"RHETORIC" WITHOUT DIALECTIC

http://www.classicalliberalarts.com/Courses/TRIVIUM/ClassicalDialectic/index.htm

There's talk about Rhetoric, but you can't study Rhetoric without learning Dialectic first.  For proof of this we need look no further than the first line of Aristotle's The Art of Rhetoric.  He says explicitly that:

"Rhetoric is the counterpart of Dialectic."

The art of Dialectic (as well as Grammar) is assumed knowledge in any classical book on Rhetoric, yet students are offered courses in Rhetoric without every studying Dialectic.  How can this be?