Bmats, Gretzky was a phenomenon the second he entered the league. Hell, the game's rules had to be changed for him, he was that dominant. And even still there's debate around who's better either Orr or Howe or Gretzky.
Jordan though was coddled and protected by the NBA. Now, Stan makes a good point. If you're retiring Jordan why not guys like Russell, Robertson etc. who were just as dominant and considered the best?
Also, the phenomenon of Jordan came at the right time. Globalization and the television along with the breaking down of communism and opening up the world even more, all contributed to the world wide growth of Jordan which was assisted by the new and rising company Nike who with their marketing power accompanied with the NBA were able to take full advantage. I believe this is why so many people view him as the all time best because this never existed for any of the other players. If it didn't, then I think the way we view him would be vastly different. With Gretzky, it's different because we as Canadians and Americans to an extent recognize hockey as a regional sport and have grown up with many of the players. Its why we see a guy like Ovechkin as a notch below Gretzky and know it when we see it. In Europe, I wonder how big Gretzky even is because I guys like Jagr and Tretiak can be considered just as good (depending on context).