Given that the Control class implements IDisposable, I would think that ASP.Net is at least capable of triggering a Dispose cascade as the Page finishes it\'s life-cycle on
No, you should not call Dispose on controls, that is being done. You are responsible for other Disposable objects you create outside the Control structure (FileStreams etc).
This follows from a general .NET principle: The Page is the owner of the Controls and therefore required to cascade the (explicit) Dispose to them. For the actual code you will have to Reflector the code for Web.UI.Control.