Just he wasn't fit? Lol, that is a huge difference, it's not "just". There are plenty of perennial underachievers who could do wonders, if only they weren't gassed out after one set of tennis
Besides, Nadal was already multi-slam winner in 2008, while Novak was just breaking through, he didn't have experience and was still developing far more than Nadal.
Bottom line, while Novak is certainly not "invincible", it's obvious that this matchup is on his racquet now, not on Nadal's like it used to be in the past. 
you don't seem to get it.......what i mean by saying that he is "just" more fitter these days is that he isn't necessarily playing as well as he did in 2008, but is really cashing in on nadal's drop in level.......anybody can see that.......i said the same last year as well.......nadal dropped his level and djokovic just upped his fitness level......
remember that i am not making an excuse for rafa's results but rather making a strong
positive case for rafa hitting back at djokovic! unlike the fedtard argument which always reflected excuses for every defeat and sounded like every defeat should be discounted for the reasons they state.......so there's a difference.......
djokovic's fitness struggle was a non factor against rafa in 2008 because rafa was thrice the player in 2008 than he is now and used to put the matches to bed before djokovic even got into the match.......djokovic squashed players like peak david ferrer 1, 3, 2 in 2008 AO.......against the same player at 30 years of age in 2012, he was on the brink of collapsing like in the murray match.......that alone should tell you that djokovic has simply shifted his game more towards defense and fitness.......
nadal din't allow him a sniff in any of their slam contests in 2008 and 2010(i will exclude 2006 and 2007 so that you don't complaint), something which even this so called version 2.0 of nole couldn't do to nadal in any slam.......djokovic only barely got past nadal yesterday who's clearly playing at a level or two below of what he is capable of.......
there is no such thing as match up, it's all subjective nonsense.......even if i am the only one standing on that viewpoint, i will believe it.......what if nadal starts striking his backhand like in 2010 and cuts down the errors? will he suddenly possess the match up advantage?
that's why there is no such thing as match up.......it's all relative like everything else in this world.......whoever first said that tennis is all about match ups is an utter clown.......
i will say this - "tennis is all about adaptability"........whoever adapts better is the winner.......