A combat round is six-seconds long, and if you've ever trained in an European Martial Art or an Asian Marital Art, it shoudl be obvious that a six-second MUST include more than one blow. Which the game designer's all admit it does.
It is more than possible to kill two opponents inside of six-seconds with any weapon. You just have to know what your doing!
Now, not to go all Medival Historian on you, but...
Hans Talhoffer wrote an exacting manual of German medival/renessance combat during the 15th century. He actually tought and fought in the major wars of the time. The game you and I play on the weekends, he lived.
His manual includes a chapter on the pole-axe, and having been at the recieving end of some of this (I'm an
ARMA freak, in additon to DnD Geek), I must say it is more than possible to cleave with any weapon in the DnD game, polearms and spears especially.