I was at Red Rocks on Friday too. Coldplay made mention of it on Thursday (and included some song lyrics and guitar riffs).
The reason I went to see Coldplay at Red Rocks is because as long as I can remember, I have wanted to go there because of U2 (probably 1985 or so). It was hell of an experience - seeing the venue live and in person. Imagining a young U2 on the stage.
In fact, Friday - it was even rainy - jsut like the U2 show.
Management at Red Rocks told me that they asked U2 back for the anniversary, and to Red Rocks dissapointment, U2 declined.