Okay, he's entitled to hate Slumdog and the book on which it was based because the story violates the oath all writers take so their readers will be able to suspend disbelief and go along for the ride...that oath being, of course, that the happy ending can't hinge on a multi-part Deus machina.
The thing of it is, though, is that very oath is the reason most of us give our books tragic endings. Happy endings in life ARE DEPENDENT on the Deus machina, the coincidence, good luck. The laws of probability, after all, work against happy endings. Misery is our lot, by and large.
And we, as a country, as a planet, needed a movie with an improbable happy ending. We've seen the dramas where the lovers don't get together in the end. It's called Romeo & Juliet. It's called Atonement. It's called every single drama ever. This was a fairy tale pretending to be a drama. Rushdie has a problem with that, fine. I loved the movie because it wasn't afraid to have its poor, luckless souls get a break at the end. It happens sometimes, and it gave me hope. That's a good enough standard for a movie as any I can think up. So there.