If you didn't notice, they're not too afraid of him prior to ESB. The Empire is, well, an Empire. As long as the likes of Tarkin, Yularen, and Thrawn (and even Xizor) are around, Vader isn't the unchallenged top dog. He may be the emperor's enforcer, but he has peers who also have Palpy's favor. People he can't move against without really good reasons.
If you didn't notice, they're not too afraid of him prior to ESB. The Empire is, well, an Empire. As long as the likes of Tarkin, Yularen, and Thrawn (and even Xizor) are around, Vader isn't the unchallenged top dog. He may be the emperor's enforcer, but he has peers who also have Palpy's favor. People he can't move against without really good reasons.
Well yeah. Some people Vader can't just out and out kill on a whim. But I don't think even though brought up Vader's name to him.