The Arma III Website has an update from Bohemia Interactive Studios on the animations in their upcoming military shooter sequel, describing how they are using three optical motion capture systems, including high-end Raptor-4 cameras from Motion Analysis Corp (thanks Slippery_Jim). They offer an interview with Zdeněk Vespalec, talking with the game's animation lead, and offer this trailer showing how this all looks in the game.
That bothered me too, all the soldiers have the same gait. For a bit I thought they were all synchronised, like how each soldier in a unit in Total War used to be at exactly the same animation frame.
The movement (which is indeed a separate thing to animation) always bothered me. I know turning instantly isn't realistic enough but Arma and Op-FP1 both felt wrong. Turning off the mechanism where your aim would move before your body when you turn helps, but not enough.
"The only thing necessary for the triumph of evil is for good men to do nothing." - Edmund Burke