It's a shame that Nadal, after flying all the way down to Australia and also flying from Brisbane to Melbourne, has to pull out after yet getting injured so early on during his comeback.
Clearly though the priority for him this season was going to be remaining healthy enough to enter the big tournaments on clay, notably Roland Garros, the Olympics (at Roland Garros), and probably the tournaments in Spain as well (especially Barcelona which means more to him than Madrid). From a British perspective, I'd love to see him at Wimbledon one last time as well.
His body has taken an absolute pounding during his career, and whether it holds enough across best of 5 set matches and numerous tournaments still remains to be seen.
Other than the grand slams and a single lead up tournament before each of them, I always thought he should limit his activity on hard courts (which are rougher on the body than clay or grass) anyway. I saw that is next scheduled to be Dubai, when I thought that if he is fit enough to play at all during that period a South American clay court event surely would have been a better choice. And at this stage of his career, Indian Wells and Miami, which lead up to nothing, are a waste of time. I'd argue that they're a waste of time for Djokovic as well - he really wanted to play in those events last year, but couldn't as he wasn't allowed to enter the US at the time, which IMO benefited him and his title chances at Roland Garros (the 'enforced' break did him good).