It's not a first-come first-served. The biggest generally aren't any more, unless they;re trying to make some sort of headline like "Wiggleyourlittletitsandshoutloudly's gig sold out in 4 nanaoseconds!". The Zeppelin gig, just like Glastonbury, was done on a lottery system. People entered, the people were drawn, then they had the oppertunity to pay. Anyone could have won it, from anywhere in the world.