Football is a game of attrition. A good GM will build a roster to cope with that, even in the extereme, and going into a new year won't just be guessing that "our luck will turn" and everyone will be healthy.
Players getting hurt are in part the GM's fault if nobody is there to pick up the slack. Drafting guys whose interest in football is so low that they'd rather play video games than practice is the GM's fault.
Did injuries kill the Packers last year? I believe they were way up there on the most players on IR / most starters lost/ most starting player games lost stats.
Most NFL teams have significant injuries and have to go on into the playoffs without a dozen or more guys that they were counting on. What is really odd is when one of those teams publicly whines about it, from the owner on down to the last player on the bench.