I think (and I admit I haven't checked recently) that the film was based on a short story by ACC (called The Sentinel ?) and the novel was written after/during the film was made, from the screenplay. I'm sure he had a lot of input though. So I agree with your point.
There are a number of BIG differences between the film and the book too.
- Top Gear Tigers and Bingo Boilers: Farewell then, Phones4U
- Breaking Fad 4K-ing excellent TV is on its way ... in its own sweet time, natch
- First Irish boy band U2. Now Apple pushes ANOTHER thing into iPhones, iPods, iPads
- Updated iOS 8 Healthkit gets a bug SO Apple KILLS it. That's real healthcare!
- Stephen Pie iPhone 6: Most exquisite MOBILE? NO, it's the Most Exquisite THING. EVER