You're video of 10/11 is w/o backing track as well. He kinda shortens and extends a few of those chorus notes. That, or they turned the backing track way down.
Also, what's up with the dude dancing in that vid with the 2 middle fingers waving. He's totally into the show, and flicking them off at the same time.
As far a triggering the backing tracks, having them set from the start of the song is possible, but as you said, 1 slip of a beat and everything is off.
This means U2 would have to play perfect time, all the time. I'd always guessed Edge triggerd them with a foot switch.
So, U2 playing with backing tracks actually makes them better, cause there's no margin for error.