I don't know but I'd guess that it gets the info directly from BIOS and/or HAL, a plug and play sort of thing with the OS knowing and comminucating to the hardware and all. WMI is just a API layer to access that info. I'd assume a new version of SMS to heavily rely on that for hardware and asset inventory.
As for your problems with the code, I really don't understand why you have these problems, perhaps the BIOS needs an update, or is is a permissions sort of thing.
