Nadal is closing the gap on grass. If he hadnt called the trainer during the 5th set, he would have a great chance of winning it. The first few posts say that Nadal won the French Open while Federer had his slump, but lets not forget that Nadal was physically drained going into the Hamburg final, and on a larger scale, the whole of the hard court season.
If he can't manage his season to play a full year, OR if he's just smart - he knows his only real chances are on clay so he plays a million matches in the first half and then is asleep / injured for the second half... that's up to him. Two W finals = genuine grass contender. Two years of winning nothing in the second half of the year = non-genuine competitor over that period.