Five days later both will appear as headline acts in the pop industry's latest attempt to save the world, NetAid, to be broadcast live on TV and the internet for the benefit of war victims in Kosovo and Sudan. It is billed modestly as "the most extraordinary coming together of international superstars in history" which will be seen "by more people than any other concert before it".
Even the most altruistic observer could be forgiven for asking the question: are these facts in any way connected? For the more cynical, it looks like yet another example of fading stars using the feel-good medium of charitable works to boost or rescue their careers.
The whole business, of course, goes back to Live Aid in 1985, when Saint Bob Geldof marshalled the music industry's finest in the cause of Africa's starving millions. While few would doubt the motivation behind that enterprise, it did give the bands and their record company executives an energising glimpse of what that kind of exposure could deliver. And many of those who took part on that memorable day have, off and on, been at it ever since.
From the Mandela concerts to Amnesty bashes, the likes of Bowie, Peter Gabriel and Sting have been in and out of the star-studded line-ups. No fewer than seven of the original cast of '85 are lined up for the three linked NetAid concerts in London, New York and Geneva.
Among the many beneficiaries from Live Aid, Queen effectively re-launched themselves with a spectacular set which put them back in the stadium rock big-time. Madonna signalled her arrival on the world stage, while U2 were lifted from underground heroes to global megastars and all their previous albums re-entered the Top 40. Bowie, linking up with Mick Jagger for a version of "Dancing in the Street", went to number one in the singles charts - a position he has not held since.
But the most spectacular instant success story was that of Tracy Chapman after her performance in the 1988 Nelson Mandela 70th birthday concert at Wembley. Previously a virtual unknown, a week later her debut album leapt to number two in the charts before going on to top slot both in Britain and America and selling two million copies.
When another Wembley date was organised in 1990 to celebrate Mandela's release from prison, retailers were confidently predicting that Bonnie Raitt, who had just released Nick of Time, would have a similar impact. An advertisement by WEA records in the trade magazine Music Week at the time offered advice on how to "make Nelson Mandela work in your shop". It then revealed that Nelson would do the job for them if they stocked up on four records featuring WEA artists who were on the bill.
George Michael, who fronted this month's NetAid launch and "let slip" that he had personally donated pounds 500,000 to the cause, has also much to be grateful for. Singing with Elton John at Live Aid marked the beginning of his transformation from Wham! pretty boy to serious voice, and the Mandela concert confirmed his position as a solo act.
Hugh Masekela, the formerly exiled South African trumpeter, pulled out of the 1990 Mandela concert on the grounds that it was being used by white musicians to sell their records instead of promoting African acts.
Annie Lennox, the re-emerging singing half of the Eurythmics, said afterwards that performing in the first Mandela line-up had been the "proudest moment in my career". But her memorable duet of "Under Pressure" with Bowie in the 1992 Freddie Mercury event apparently did her a lot more good. It came as she was launching out on her solo career and her single "Why" was still in the charts.
Her ideological commitment, however, remains undimmed. The new single is the aptly named "I Saved the World", and all ticket and merchandising proceeds from the Eurythmics' forthcoming world tour are going to Greenpeace and Amnesty International.
If the record industry has done well out of all these virtuous impulses, it is not a situation that executives expect to go on indefinitely. One executive went so far as to declare last rites on the whole idea: "This could well be the last glimmering of an idea that has really had its day."
Live Aid 13/7/85: David Bowie, Eric Clapton, George Michael, Elton John, U2, Sting, Bryan Adams, Bryan Ferry, Jimmy Page
Mandela 70th Birthday Tribute 11/6/88: Eric Clapton, George Michael, the Eurythmics, Peter Gabriel, Sting, Tracy Chapman
Amnesty International Human Rights Now! Tour 1988: Sting, Peter Gabriel, Tracy Chapman
Mandela Tribute 16/4/90: Peter Gabriel, Bonnie Raitt, Tracy Chapman
Freddie Mercury Tribute 20/4/92: David Bowie, Annie Lennox, Elton John, George Michael
NetAid 9/10/99: David Bowie, the Eurythmics, George Michael, Bryan Adams, Jimmy Page, Bryan Ferry, Sting, Bono