But Wait a Minute ...
The electromagnetic pulse didn't just knock out power in the casino; when they set it off, there's a quick shot of the entire city of Las Vegas going dark. The movie then cuts to the inside of the casino they're robbing, where we see people trying to steal chips at the black jack table, and other fun varieties of chaos they intended. So how did the rest of the city do?
Well, keep in mind that according to our merry band of thieves, the electromagnetic pulse doesn't just turn the lights off -- it shuts down every power source within it's blast radius. When the plan is devised, we're told the city will temporarily be plunged into the 17th Century, which is great if you're stealing money, and bad news if you're, say, on life support in a hospital.
Hospitals have back up systems that come on during a power outage, but so do casinos. The pinch is being used because it takes those out. Hell, if we're talking every power source, everyone with a pacemaker is dead on the spot. But at least they weren't one of the poor bastards in helicopters and passenger planes, now making an increasingly less-than gradual descent into Las Vegas.
According to Ocean's Eleven, the biggest danger is chorus lines veering off course, kicking thousands of audience members to death.