Economy of scale... pure and simple. When 3 million people WANT to see you play in a year, you CAN'T play small clubs (do the math).

When jazz musicians have audiences that large, they'll play stadiums, too. I seem to recall Montreaux or Newport Jazzfest getting pretty big, but that's ONE WEEK. These guys pull that number twice a week

Anyway, this is not unique in any way. Anyone remember the scale of ELP's touring rig? Stadium rock is its' own experience. No, it's not a theater or a small club. It is its' own musical experience, different, but still enjoyable. Like seeing a small high school football match, then going to see a huge college or pro game. Same game, utterly different experience...

I have a feeling that, at this point in U2's career, that they aren't all that desperate to make money Playing to the most people, letting the majority of their fans that WANT to see them be able to, even if it means a lumbering, expensive touring system, seems fair enough...

Trust me, music all through the ages has been about money as well as art. Mozart, Beethoven, Verdi, none of these guys were immune to the commercial considerations of actually making MONEY while trying to produce 'art'.... This is more of the same, just ramped up for 21st C technology. I guarantee Liszt would have played to this number of people if he could have!