I totally agree. Ideally, the sub-products within Object Desktop, such as Start10 would never ask you for a serial once you enter the serial for Object Desktop.
The My Downloads page of the Stardock.com store shows Object Desktop, and the products that are "included", but makes no reference to re-using the Object Desktop serial to authorize various sub-products.
A simple statement such as:
Your Object Dekstop serial number is used to authorize ALL of the following products
would be helpful.