The lowest level managing directors typically have several additional managing directors between them and the C level executives. In other words, you can be in charge of a 15 person unit and be called a managing director or you can be in charge of an entire division of 500 people and make as much as some fortune 500 CEOs and be called a managing director. Generally, your clients are fairly sophisticated and know exactly where you are in the totem pole.
In addition to just being a rung on the ladder, the VP title often also means that you are a corporate officer, who can enter into agreements on behalf of the company.