Why a Happy Ending?

I was not surprised that the ending would be a happy one. Just look at the setting. He lives in a relatively nice home, his son is going to baseball practice, he has a daughter, a dog, and a cat. And from the interactions that he has with his family it is clear that he is genuinely happy.
I do, however, find it interesting that the author chooses to inform us that the story does indeed have a happy ending. I think that this is a very deliberate action on his part, with the intent of having you read the story in that light. If a story has a happy ending, and you know about it beforehand you read the story differently. By the same token, if you know that the story has an unhappy ending, you also read it differently. You look at every bit of material in a different light. You look at things and say to yourself, "Oh, yeah, I can see how that's going to bite you in the butt." Whereas if you read a story and you know it has a happy ending, even when things go wrong you look at it and say, "Oh no, but it's okay, it'll all work out in the end."
You really do read it differently. I believe that it is the authors way of doing what parents do for little kids when they say, "Now, this movie has some scary parts in it, but remember, it's only a movie, it's just people wearing costumes and playing pretend, okay." Of course the context is a bit different, but you understand my point.
All in all, I thought that it was a very clever and intriguing literary device.