Pretty much all shoes offer some measure of stability. Neutral shoes may not have a medial post, but they still have some type of support. A lot of shoes have a plastic plate for torsional stability, many have a heel counter (some stiffer than others), etc. For example, take a pair of Nike Pegasus and compare them to a pair of Brooks Ghosts. The Ghost is a more stable shoe, with more torsional control and a stronger heel counter than the Pegasus, even though both are classified as neutral shoes. Now compare both to the Mizuno Universe. The Universe has way less torsional support than both, and doesn't seem to have much of a heel counter at all.