Roger's shots are an example of the kinetic chain, all he does is conserve energy and set himself up for the next shot without having to run so much.
Also he has the one handed advantage of being versatile with the shot, he can slice, dropshot, volley with it pretty well and it's hard to read what he's going to do next with that because you don't get the tell-tale letting go of the handle with the other hand moment that you do with two handers.
Of course this doesn't help him when he gets shoulder high balls with lots of topspin but that's a particular match-up issue more than anything else.
Rafa's backhand is a great defensive shot when he's confident but it has never been the centre of his attacking game, once the weaknesses on it are exposed, he's left without a wing practically speaking, nowadays it is a garbage shot (when was the last time he hit REALLY deep with it DTL?) and he's running around it to hit his FH.
Nalbandian's BH is like Roger's FH, a perfect example of kinetic chain and how to put all your power behind one shot without too much effort on your own part.
Another great BH was Safin's when on, he hit the ball so cleanly off that wing.