They offer it because they make money on it. Most people with rack up interest charges and that is how it is worth it for them. Most people spend more because they justify it in their head and that is why they can afford to do this. They do follow through with giving you the points. I did it and there were no tricks.
Like I said, I do it. The only negative is the annual rate, but I know that I save more than that with our yearly trip to see family. Since all of our extended family is on the other side of the country, we really feel that this is a must expense for us.