Don't look into the stance too much. Like I said, that was one little microcosm of Greco-Roman to illustrate a point about imagination and conception, much like car pushing. But at the same time, the position of the feet are not integral to the stability of that configuration in the forward and back directions. You can go uneven, or go parallel, and maybe you gain some extra stability by going uneven, but traded for mobility, and on the other hand, the difference in stability is not enough to make or break stability there if you understand the basic ideas behind how to make that movement work.
Indeed. One exercise is to have someone continue to push you while you pick up one foot or the other, then while you move forward. (Have them take their hand away suddenly to see if you're leaning!)