Tip, in visual studio when you see a class that looks unfamiliar, type it out into the code editor then right click and choose "Go To Definition" or click on the text and press F12. This will take you to a window that shows how the class is seen by reflection.
In this case you can see the DrawableGameComponent class inherits the GameComponent class, and the IDrawable interface. So basically it's a derivative of the GameComponent class that implements methods found in IDrawable including the Draw method. This however doesn't meant it's the only one you can use, in fact you could write your own version of DrawableGameComponent that includes your own set of methods, the XNA team created this class as a prefabricated example of how to make a customized GameComponent
Edited by AmzBee, 17 July 2013 - 12:11 AM.