My ab initio instructor summed it up thus:
"If, when the fish pie hits the strawberry cheesecake, you are found to have been following the POH to the letter you will be exonerated. On the other hand if you are found NOT to have been following the POH to the letter you probably will not, regardless of circumstance"
I do not have either the experience nor the expertise to say whether or not ALL POH's are accurate and correct to the final punctuation mark, but the little experience and minimal expertise I DO have suggests to me that if you operate the aircraft within the boundaries laid out by the POH then there is probably sufficient margin for error as to keep you out of trouble. After all; the writers of the POH have their own reputations (not to mention liability suits) to worry about.
WD