Just seen the advert for this event and although I feel it will significantly help in showing the vermin terrorists we won't give in, a part of me feels its also part Shameless PR from the companies that operate in behalf of these music artists..
Record label PR dept: "quick, quick, get Chris Martin in on this tragedy, post on twitter a thoughtful quote, and sign him up to the tribute gig"
Record label ceo: "Yes, I agree, that will bolster his profile in the youth demographic tremendously and sales will shoot through the roof"