These players aren't spamming. They're selecting individual unit abilities within multiple control groups and switching off the membership of said groups in real-time.
That documentary clip is somewhat misleading. Some very strategic top-level Starcraft players with excellent micro-control can have as low as 200-250 APM. Some macro-oriented players such as Bisu ( http://en.wikipedia.org/wiki/Kim_Taek-Yong ) have ~420 APM.
Though APM is a datum which has grown during the evolution of the game, Flash ( http://en.wikipedia.org/wiki/Lee_Young-Ho ) ,the current highest ranked Starcraft player in the world, only has "average" APM for a pro gamer.
At the pro level, success is less about "action volume" and more about which actions one chooses to take.