I looked at the Wikipedia entry for their 2007-08 tour and was shocked at the level of venues they were playing. Multiple nights at the Staples Center, Air Canada Centre, Nassau Coliseum. They did two nights at the Prudential Center and then immediately followed it with a show at the Izod Center, then did MSG a week later which is a very impressive level of demand. I'm not at all surprised that they did so well in the U.K. but I just wasn't aware that there was so much Spice Girls nostalgia in North America in 2008. Usually it takes longer for an act like that to come back to such prominence.