Ozzy has always let it be known that Steve Vai was THE guitarist he wanted to work with. They wrote and recorded the original 'Ozzmosis' album and were set to go when Sony basically told Ozzy they wouldn't release the album as is - probably because it was not 'contemporary' enough, i.e. too 80's sounding (this was when grunge was king, of course). I think one or two of those songs ended up getting reworked for the actiual release, so it is only natural that they would have a lot of stuff left over from those sessions. I'm sure there will be an Ozzy/Vai album one of these days - the question is when.