Really? why would that be, U2 has employed this method on most of their tours. Most acts do. I know for a fact the stadium shows this summer there will be two stages. There are two for the arena stages also. Some of the technical gear though there is only one, those get taken down first and shipped immediately to the next venue where the other stage is already being set up. There were 3 JT stages, 2 Zoo stages ( 2 indoor and 2 outdoor) and 2 Popmart stages also. In fact the only thing that there was not a duplicate of for Popmart was the screen and the lemon. Those were always taken down first though and shipped immediately to the next stage.
The other thing is they may be practicing breaking down and resetting in a short time frame, so they could take the same stage in LA and set it up in SD. The SD arena though has an event at it on Sunday. So they wont be able to start until late Sunday night or early monday morning anyway.