[source: BBC News]
In a competitive market, with variable prices, high demand pushes up the price which then triggers further supply. In a closed market, with fixed prices, high demand may have the paradoxical effect of reducing supply.
If the Spice Girls earn more than they expected from the first few concerts, this might have motivated them to put on even more concerts. On the other hand, it might mean they can't be bothered even to complete the concerts that were on the schedule.
And of course we should always question the data. What exactly is meant by the word "phenomenal"? Does it mean surprisingly high ... or surprisingly low? Here's what Wikipedia has to say on the subject of Anomalous Phenomena.
"Purported phenomena with explanations considered to be outside the scope of conventional science can be classified as paranormal phenomena. Because these anomalies are difficult to explain in terms of science, their existence is often challenged by skeptics."