We pitted an AT&T iPhone 4S vs an AT&T iPhone 4 to compare the death grip attenuation and when we tried to choke the 4S, it didn't budge. The 5 bars stayed steady throughout our entire test. The old iPhone 4? When gripped, the signal slowly dropped from 5 bars to 3 (and then re-gained those lost bars when we opened it up).
So if you were worried about the Death Grip still existing in the iPhone 4S, worry no more. It's gone. Sayonara. Killed. Buh-byed. Dead dead dead. You can't "hold it wrong" anymore. Finally?