Even in the OT (not considering the prequels at all), Vader's right arm is robotic, we know for a fact. If we take the ROTJ visual "skeleton" glow as some kind of guide, apparently both his hands are robotic (even if his right arm is mostly real). But if you watch the scene frame by frame, he blocks it with both hands, and some of the shots hit his glove and disappear in a puff of smoke/sparks, while others bounce off and hit the walls. Maybe some combination of force and physical blocking?
I don't know about this "Mandalorian gauntlet" thing of course, having washed my hands of the EU stuff long ago (other than the PC games). It appears he's just wearing leather gloves over his robot hands.
I sort of assumed for the longest time it was just that Vader's armor protects him. But then when you consider that the suit appears to be mostly leather (not even the kind of full coverage offered by the "useless" Stormtrooper armor; please note that Vader's shoulder armor deflects a lightsaber blow from Luke in ESB!), I guess you might say it was some kind of Force ability he used (going just by the movies here, since the EU will tell you whatever).
Maybe it's some kind of "energy dampening cloth"? Sci Fi tech does have that sort of thing too... and maybe it's just really expensive, explaining why everyone doesn't cover themselves with it.
I think stylistically it was just meant to show that Vader was more dangerous than the average bad guy, and show why the good guys couldn't just gun him down.
I suppose having it be a "force powered block" would further emphasize that Solo is in over his head (remember, this is the guy who poo-pooed the Jedi and the Force in the previous movie), where his simple, naturalistic, technology-based methods of fighting aren't adequate for this situation. He's dealing with the Dark Lord of the Sith, now.