The stories are parallell explainations. Two different possible stories for what have happened. The book doesn't point to either one being true or false. Pi himself goes out of his way to present the 'realistic' story as an alternative that is easier for the interegators to accept.
The point of the book is not to decide which story is true and which one is not really. Neither is it a defence for religious delusion as someone else says in this thread. The point of the book is basically what thew author says, if you look for the realistic and 'true' in everything you miss the better story.
I think anyone can agree that the story about the animals is more compelling than the grim and realistic account of the mad chef and the wild supressed nature of Pi. So when the author says that the book is a story that will make you want to believe in God, this is what he alludes to. You want the story of the tiger to be true, because it is a much better story. Applying this to other aspects of life the message of the book basically says that if you only focusing on 'facts', 'scientific explanantion' and such presise explanations of things you will miss the better story.
I think the book is great, and accomplishes it's goal in wanting you to believe the story of Richard Parker.
