I think it's more of the understanding on how the two vastly different pieces view the environment, and what they each can see.  Windows still, as far as I can tell, doesn't properly report Zero pages, it just kinda lumps that into Free/Cache, which is a misnomer in itself within Windows.  Plus, you get some applications (looking at you SQL Server) that will consume all available memory unless otherwise told not to, and writes random junk to the memory addresses it's not actually using so that it doesn't get marked as Zero page by the hypervisor and used somewhere else.  This has the effect of reserving the memory, but screws up reporting horribly when trying to right-size the environment.