Magento: What are the empty EAV setup classes for?
===

There are lots of descendants of `Mage_Eav_Model_Entity_Setup` for example


    class Mage_Checkout_Model_Resource_Setup extends Mage_Eav_Model_Entity_Setup
    {
    }

But all of them are empty.

What is the use of having all these empty classes?

Is it just for the sake of extensibiliy and to keep common functions that are shared in different setup scripts of the same module?

I was thinking there might be some kind of module autodetection triggered by these custom classes, but could not find any hints into this direction). 

(Based on Magento Certification Study Guide: What are the advantages of using a custom setup class for manipulating EAV attributes in a custom module).