I see what you mean. Building a FF-style menu might sound easy, but it's quite complicated and (most of all) can't serve as a template for others to use. The idea is to have a simple template with code that can be easily understood and then build on it, rather than having a custom, complex solution in place.

An easy method of implementing drag-and-drop inventories is to use a separate view for the inventory and actual 3D entities that can easily be touched, dragged, dropped, etc.