Mike has NOT sold 18million albums worldwide, so they must be including other artists. It is possible though, that they have SHIPPED 18 million MJ albums because Sony announced on 21st July they had shipped 15.5million MJ albums at that time. I'm surprised they would ship more because according to the best estimates Mike has sold around 9 - 10 million this year and so it wouldn't be necessary to ship more just yet with another 5 - 6 million sitting on shelves.
Also, I find it odd that they couldn't get the involvement of any big stars in a MJ tribute concert. To me that is disgusting. I would certainly expect JT, Beyonce, Kanye, Usher, Ne yo, Chris Brown, R Kelly, Snoop, PCD, P Diddy and many more to jump at the chance. Perhaps August was too short notice for many of them. I hope somebody will do a tribute concert at some point and also a tribute album too!