I think his reactions make dramatic sense. To a person who has only seen the original SW and is now seeing ESB for the first time (let's all try really hard to imagine that) it gives you the impression that Luke might actually pull this off.
Regarding Dooku's reaction to having both hands cut off vs. Luke's reaction in ESB: I would imagine that a screaming Dooku in that scene might have pushed the film into "R" rating territory.