Oh yes, it's a can of worms this topic and the study has already caused some quite heated responses.
Certainly diet or keeping your dog lean and trim can help delay the onset of hip dysplasia by a substantial number of years however it's not the underlying cause. It's not terribly ground breaking, but the study is useful for owners to realise they can give their dogs up to apparently six years more pain free life than would be the case if they allowed their dogs to gain any unnecessary weight. Same as humans.
A further article and debate on this subject here.
Same as us you don't have to necessary be over weight to be a victim either, though. Other breeds, unlike Labradors who don't suffer quite so much from weight gain, be it genetical or environmental, generally are still susceptible to the disease. So the "study" doesn't prove in any way at all diet is the key issue in dogs because they don't use any of these as control groups which would in all probability prove the theory palliative at best.
It is key in Labradors who suffer high incidences of the disease and who are it must be said prone to weight gain in delaying early onset and severity, but not unfortunately a cure in reducing the incidences in the breed or in any other......breeding cleaner and cleaner dogs and outcrossing to other breeds or types to reintroduce vigour and genetic soundness for the disease where urgently neccesary is still it seems the only reliable cure.
There is that chance the study can be misinterpreted as being "the cure" by reckless breeders and purity worshippers, and for them to pass the buck back onto unwitting owners, so the study should really have made that plainer and not introduced any possible confusion by trying to reduce the genetic component involved.