Why does Hudson only ask for certain extension points?

MyExtensionFinder.java

@Extension
public class MyExtensionFinder extends ExtensionFinder {

	public <T> Collection<ExtensionComponent<T>> find(Class<T> tClass, Hudson hudson) {
		System.out.printf("find(%s)\n", tClass.getName());
		return new ArrayList<ExtensionComponent<T>>();
	}
}

/**
 * When this class is loaded and invoked it produces the following output.
 *
 *
 * find(hudson.model.listeners.SaveableListener)
 * find(hudson.model.TransientProjectActionFactory)
 * find(hudson.model.AdministrativeMonitor)
 * find(hudson.model.queue.QueueSorter)
 * find(hudson.model.Descriptor)
 * find(hudson.model.PeriodicWork)
 * find(hudson.model.LabelFinder)
 * find(hudson.model.RootAction)
 * find(hudson.slaves.ComputerListener)
 * find(hudson.model.listeners.ItemListener)
 *
 * After accessing a web page, it calls for the following extension points
 *
 * find(hudson.widgets.Widget)
 * find(hudson.model.DownloadService$Downloadable)
 * find(hudson.model.ManagementLink)
 *
 *
 * This is only a very small subset of the actual extension points available
 * (and virtually none of the extension points that that I'm interested in)
 * http://wiki.hudson-ci.org/display/HUDSON/Extension+points
 * Any way to see the full set?
 */