Nadal is not a coward, but he did not achieve what he did because he is not smart enough. Therefore, based on his first hand knowledge and experience on the matter, the only logical explanation is that he knows what casual observer and many 'experts' don't, obviously. He has to play these matches against Djokovic while world is watching and his face simply reflected he knew what he was up against, and the most likely outcome.
We don't have to face Djokovic. We simply expect/request - glorious entertainment, an 'epic one', as if we are entitled to have it. Hence, this casual, carefree 'too much'.
Surely, RG19 will be more fun.