You gotta remember that Nadal often starts slowly in any given tournament. By the latter stages, he has warmed up.
Look at RG 2011 when he nearly lost to Isner in the first round (I think). Obviously at Wim, the slower surface in the 2nd week helps as well, but if someone takes him to 5 at Wim, it's because they're playing out of their skin more than anything else.
Jo served pretty well at last year's Wim QF
The let-down against Nole was inevitable, and not due to court speed.