Eh, if it says it is a magic item you don't really have a case against it being even if you think the intent was there. It is a magic item that basically becomes the BSB. GW could have simply said at the start of his rules section that he counted as the BSB as well, but they didn't, they chose to make the BSB a magic item. I say as strange as it sounds, it can be destroyed by Vaul's.