The argument that "everyone has a DVD player" is bull.
True, most (if not all) gamers own at least one DVD player in their house. However, perhaps the room where the Wii is located does not have a DVD player also. Maybe it would just be more convenient to be able to play DVDs on the Wii so that you can remove the DVD Player box from your television stand. There are several factors why gamers would want DVD capabilites on their Wii.
In my case, I'm living in an apartment with three other blokes. We have a 30" flatscreen in the living room with a DVD player, cable box, and PS3. However, in my bedroom I only have a 14" television, my Wii, and no DVD player. I have to play DVDs from my laptop everytime I want to watch something from bed.
That being said, I would very much appreciate a firmware update.