for at least the last few tours, if not longer, GA/field/pit tickets for U2 have been cheaper than the best seats immediately behind them.
i suspect the idea is to cater to two different classes of fan: calmer, better off financially, and seeking comfort/defined space, VS. younger, less affluent, rabid, willing to be packed in shoulder-to-shoulder.
in other words, they pack the pit with the kind of fans that an ego-driven rock star like bono is going to want right in front of him