Yeah, that's one key difference between the modern mechanics Federer uses and the classical stuff Sampras does. Fed, like most players today, needs to rotate his torso significantly in order to initiate the swing. But, then again, for also that reason, he can generate lots of power without moving his legs a lot. In any case, it means that you have to have excellent footwork to crank balls accurately on the run, which Fed can do.
It's just with Sampras, he can run full-force and use that speed to whip on the ball. His stance can kinda float between pure closed and neutral, but his whiplike delivery isn't dependent on that. As, again, most old-school pros who use classical form can to some degree in a proper game. The more extreme grip are even more limited in the sense that if they chase a ball down the run, they need the ball at a certain rise in order to hit the ball cleanly. If they run into a ball, they have to time it perfectly.