But you know, there may be another reason for this as well... for all seating I mean. Perhaps some artists don't want to take any chances for accidents among fans. When people sit, it's automatically more orderly, you also don't have to queue, which matters a lot, especially if it's winter. Granted, it's really frustrating when you are trying to get the best seats, but there is a logic behind it.
I've seen shows from both points, and it's a really hard decision which I prefer - and I even saw two shows in a row at Wembley, first night was standing and second night was sitting! Standing is awesome as there's that added dimention to the show, being among fans and all, and the music "feels" completely different... but it's also tremendous stress... will I be stopped by any security dickhead before I reach the stage, how many more people are at other entrances... etc etc...
Sitting is different, much more relaxed, but it puts a damper on things when people around you sit down and you think "what the hell are you doing people?". And if you keep standing, you are blocking the view of people behind you. But your seat is guaranteed, and if you get one of the first rows on the bottom close to the stage, you will have an excellent view.
It's a tough choice. But I really like Europe for the standing shows, because of ticket prices, mostly. Much more fair.