I'm sorry but many of the responses in this thread are just plain stupid and very laughable.
I am very irritated at the kinds of resposes this thread-starter is getting.
He never asked if "cleaving" was realistic, and this thread was never meant to debate that. I feel that most of the taleworlds community is caught up in some "I feel the need to impose my historical knowledge over you" hype. Many of the responses are very disrespectful to the thread starter as well.
Look the way I see it, I think cleaving in this GAME would be a much needed and enjoyed attribute. First of all, as kahael had mentioned, in mount&blade, many of the swings do LOOK like they go through multiple people. I would feel that this may be deemed more unrealistic and unsettling the atmosphere. Second of all, as far as gameplay balance goes. Is there any reason that a player would choose to use a pole-axe or a bearded axe for any reason when a small scimitar can do roughly enough damage to kill a single unit in one hit (at a certain lvl) and yet be much faster and lighter? The pole-axe is really at a disadvantage in this. And I will argue that while you probably cannot slice through multiple opponents with it, you probably could realistically hit multiple people, whether it be with the blade, the pole, or even the guy you hit landing on other guys (and even causing a rippling effect).