As far as I can tell, it is a way for X10 to sell us something else.
If you click the help button and then click "Using the Macro Library" in the left-hand panel, it says "If you have purchased or downloaded a Macro for your library, access it by choosing "Open Macro Library" from the Edit menu."
It also says that "Macros in the Library are designed by X10 to add new specific functions to your ActiveHome system."
Smells like another "buy the add-on" to me!