Yeah, this isn't the entire rulebook. It's sort of like the Cliff's Notes online version.
The lack of a complete rulebook available to the public is why some still insist there's a hint of shadiness when it comes to officiating.
The "tuck rule", for example. Since the public had never heard of such a dumb rule and since it's never been published anywhere for the fans to see, there are still some conspiracy theorists who insist the rule was invented spur-of-the-moment to screw the Raiders over.
I still can't think of any good reason why the NFL rulebook is not available for purchase. The NFL is a money machine and you know the full rulebook, thick as it may be, would be purchased by rabid fans.
So why would the league not sell a product that a) they know they'd profit from, and b) would boost the league's integrity among the cynical?