I couldn't agree more with you're last post! Especially since, after re-watching RotS, Vader crushes the living snot out of everything in the room except Palpatine when he learns of Padme's death.
The ending of RotS, even without thinking that Vader is a Force Wuss as a cyborg, still leaves the question in my mind: What does Palpy need Vader for at this point? It seems that the Sith use a "love 'em and leave 'em" tactic against each other and that as soon as they can't use you anymore, they kill you or let you be killed. You bring up a good example of Dooku. Anyways, Palpy has control of the entire galaxy at this point and leaving Vader around only seems to be asking for a betrayal. Especially since he failed to deliver on the one promise that brought Anakin over to the dark side...
But I've already said that I don't think Vader has any reason to a) not kill Palpatine at that point or b) stay on the dark side at all as it's portrayed in L'sPT.
Xhonzi