You mean upper arm muscles are involved in everything from the elbow down.The whole point about grip and hand position is that your forearm muscles are involved in everything that happens from your elbow down, so if your hand is adopting a certain position you're putting tension on certain muscles, which should be free to propel your wrist movements.
The forearm muscles are finger + wrist muscles, muscles + have no action on the forearm itself. The upper arm muscles are elbow muscles, tasked with bending the elbow and thus moving the forearm. The back+chest muscles are upper arm muscles. If you see someone's forearm moving, then it is because of the upper arm muscles working. When you see the elbow pumping motion of the Moeller technique its because you are using your chest and back muscles to move your upper arm.
Under no circumstances should you think of any part of the arm moving by itself. Every motion, no matter how small, should be supported by the entire arm structure leading to the spine. This is how we are naturally built, and people who move really naturally - pro dancers, athletes, etc all do this very very VERY well.
Case in point. 1 minute in.
The announcer says "It really is all in the wrist" Yet you can clearly see Mike's forearms doing a LOT of moving, and his upper arms weaving back and forth as well. In order to achieve those speeds, Mike is employing his whole body naturally and effectively. Another example is this blake griffith dunk. http://www.youtube.com/watch?v=ggRqdvU6yJ8 You can see his whole body move in unison, not in separate parts.
Unfortunately, many people hear and repeat "its all in the wrist". And what many people end up doing is to try their darndest to lock the elbow in place while they practice. They tighten down their own muscles to lock something that needs to move. That means they push and pull the same joint at the same time, causing a great deal of tiredness and unnecessary stress to the joint. This ends up causing a lot of damage.
Incidentally, I can back all of this up with research. Msg if your interested in learning more. Repetitive motion injuries are somewhat of a passion of mine, and I've been studying them for years now.