Well, JeffS, I cannot but agree that if 1, 3, and 4 happened, Nintento would decreatse Wii "quality" rather han increasing. Clearly, my question could be rephrased as: "I wonder why Nintendo did not include a nice, simple but effective, not complex, dvd player".
In other words, I agree that adding any sub-par component is bad, but I was thikning of an at-par (is it correct English?) component.

Thinking of the Wii interface, adding 1 "channel" to play dvds would make it no less nice or simple or versatile, I think. Or, even just using the same channel you use for games, since you either use a game or a dvd, would have been probably even simpler.

I instead agree that 2 is generally true, and is the most likely point that made Nintendo decide against the dvd-player.

As to wanting or not wanting it, that clearly depends on a individual different needs. Who owns any home theatre system, very likely has some advanced stand alone machine and does not need Wii (or any other gaming console) as a dvd-player. Other people may want to free some shelf space, component input, or whatever, just like Tony (and me, for the record. While I don't have a home theatre system in my new apartment, I do have a € 40 dvd player, and need another one in another room. The Wii would have been a nice, simple solution).
As a matter f fact, the market for a small, nice, extra dvd player is there, so I personally do not consider this as a generally valid point for not including a dvd player in the Wii.