The dynamic roll cast Steve knows is in fact a switch cast in the Spey vernacular. In this case the line is not fully extended but left in a d-loop shape, using the grip of water's surface to provide tension against the forward cast. It differs from the roll cast in that all but the end of the line touches the water and the loop is pronounced with most of it behind the caster instead of out in front. Since this cast preceded it's new world discovery by hundreds of years, it's a switch cast
with all due respect to the Rhody Flyrodders.
When the water is used to anchor the end of the line during a change of direction the cast is known as a "single spey".
When the line is not allowed to touch the water, not left folded but extended fully into a backcast then it's often called a belgian cast by west coast us casters but once again this cast has been known as the Devon Switch and is impeccably described in Simon Gawesworth's new book, Spey Casting (chapter 13).
But the most important thing is what Pete explained - how they apply to real life fishing situations.