It's on my shelf, but I haven't gotten around to it. If it's even half as revealing as THE JAWS LOG (pretty much the greatest making-of book ever), it will be quite illuminating. I should get started on it.
It's not that rare of a phenomenon. In fact, I wouldn't be surprised if it was about 50/50 or maybe even slightly skewed in favor of the film versions.
"Jaws" the novel is a bit of a rough read. Mafia dealings (they loaned money to the mayor, and they don't want to be paid back, they want cooperation in real estate shenanigans), random drug references, a dead dolphin fetus used as shark bait (who thought that was a good idea?), etc.
Where the novel's true problem lies is in its characters. They're all either outright unlikable assholes (Quint, Hooper, Mayor Vaughn, Mrs. Brody) or ineffectual (Brody). The most valuable thing that Howard Sackler, Carl Gottlieb, John Milius, and whoever else gave notes on the thing did was to make these characters people you wanted to spend time with. Since we couldn't spend time with the shark (for various reasons), it was imperative that the audience invest in the characters. Removing the Hooper/Mrs. Brody affair, for example, did incalculable good for the story and for the characters.