This single still is from the widescreen version of ?Matriculated?, one of the Animatrix animated shorts. It has been considerably scaled back from the original material.
In the Matrix universe, the vast majority of robots fly, of hover. The runners are unusual precisely because they run. However, when you consider the maneuverability of hovering, darting robots over ground based units, the reasons become very clear.
Realistically we are a long way from being able to recreate military robots with these kinds of capabilities. The closest we have come thus far, is the nano air vehicle class, which are about the size of a hummingbird. Power, and weight requirements will keep us from creating these kinds of flying tanks, for a long, long time to come.
Link: Animatrix: Matriculated