I have two answers for you.
First, there is nothing wrong with requiring a student to get a piece of equipment if for some reason the instructor considers it necessary. I don't see any reason why an instructor couldn't require their students to get an electronic E6B. I'm mainly thinking of the independent instructors out there who set up their own training courses. If an instructor says to the beginning student, "Buy this textbook, get this video course, and get this electronic E6B," what's wrong with that? It's just part of learning to fly.
On the other hand, an instructor might work for a flight school that has a standardized kit of materials for all their students and all their instructors. In such a case the whiz wheel might be the standard, and the instructor might need to learn the whiz wheel in that case, but remember, that's for that individual program. Just because it's done that way for specific programs doesn't mean a CFI checkride should be administered in the same way.
Second, here's proof a person doesn't *really* need either type:
http://www.csgnetwork.com/e6bcalc.html
That's the site I use on a regular basis when training primary students. All the convenience of the electronic E6B with zero cost and available from anywhere with an internet connection. Plus I bet I could race you using that site and win