Interesting observation by Shawn Blanc:
"It’s interesting that the iPhone 4S, though it has an extra hour of 3G talk time, has 100 less hours of standby time."
He wondered what could the iPhone 4S be doing when "off" that the iPhone 4 does not?
I doubt it is the A5 chip since the iPad 2 manages an amazing amount of stand-by time. I wouldn’t think it was Siri’s fault – what could she be doing when you’re not talking to her? So I have no idea what would eat that many hours of standby time besides, perhaps, the battery’s actual cells being smaller so that the output of the battery is the same but the storage is reduced.