Prior to 2011, the score was 16-7 in Nadal's favor, and, I have not looked at all those matches to confirm this, but I read that broke down as follows:
9-0 on clay, 7-7 on all other surfaces, so, as is the case with somebody else I can think of, Nadal isn't dominant on ALL surfaces, just one.
Djoke is, what, 6'2", and has a two handed backhand, so the left crosscourt lefty forehand that bothers Fed so much does not bother Djoke, given that his backhand is arguably his best shot, he probably welcomes it. It's no secret that fairly tall guys with two handed backhands have enjoyed some success against him-Tsonga, Soderling, DelPotro(don't understand the Ferrer deal, and I'm guessing David may be banished from Spain if it happens again, lol). The 5-0 result THIS year, of course, IS on ALL surfaces, including 4 straight sets on Nadal's favorite surface, so that would indicate that a) previously, Djoke was neither physically or mentally tough enough, as you pointed out, to get the job done, but he IS younger, and could therefore be more expected to improve and b) given that the matches are on all surfaces, save indoor carpet, that might indicate the problem is harder to overcome than Nadal's dominance prior to this year, or, put another way, prior to this year, I'd have expected Nadal to be supremely confident vs. Djoke on dirt, on other surfaces, not so much-why should he, with a .500 record? Right now, Djoke is supremely confident vs Nadal EVERYWHERE, he's only been extended to the distance once in those five matches. In what area of the game right now is Nadal superior? Nowhere I can think of, and that includes off the ground. What's Nadal gonna do in his bread and butter area, hit even harder and make more errors, or hit with even more topspin and have more groundies land short in the court? And who has Nadal adjusted to successfully thus far, let alone adjusted to who is playing so well? Soderling, who has reached one Slam final in his career? I'd say the jury is still out on Del Potro, who is still not completely back after his year layoff and against whom Nadal had to resort to gamesmanship to beat in a fairly tough match. I think people are underestimating just how much into Nadal's head Djoke is, and an example of that is the 30-30 point in match game with Djoke serving, obviously a big point, it'll either be match point for Djoke or breaker for Nadal, and, for the first time in the entire match, Djoke plays serve and volley. Against virtually anybody else in that situation, Nadal's eyes would've gotten the size of saucers, he'd have said, "Muchos gracias!" and hit a screaming winner on the pass. Instead, he served up a high, floating meatball that Djoke knifed away for an easy volley winner, then Nadal quickly and meekly went out on match point. I'm surprised he didn't run sobbing into Uncle Phony's lap. Add to all of the above the fact that we're now in the part of the year where Nadal normally starts to exhibit "fatigue," (that is, when he's not floating stress fracture rumors along with a 6 week layoff, then retracting them), and I like his chances of prevailing against Djoke even less, if he gets to play him at all.