How did writer Simon Beaufoy come up with the concept behind Slumdog Millionaire? Why has the movie received such rave reviews?

Beaufoy answered questions about the film with Reelz Channel. Here's an excerpt from that interview:

Why do you think this movie is catching on with people?
I think this is a film about hope and overcoming the impossible. That's kind of the flavor of the movie. I think we need a film about hope, and I think maybe that is what people are responding to. There's lots of other things in it. It's in this extraordinary country, and this extraordinary city, Bombay, and it's kind of a big, operatic love story. But overall it's an incredibly optimistic story. The underdog who overcomes everything to get the love of his life, and that's very simple, and kind of sentimental, romantic. But I think we need that. We need, right now, something about hope.