I think the easiest way to prove it is to go to your local retailer and look at what's sitting next to the Wii section.
You'll probably see the DS on one side and either the 360 or PS3 on the other. Just like if you walked into the TV department you would see TV's of all sizes and prices. They are all still competitors.
People that try to show that they are not in competition with each other are just looking for a way to ignore the simple fact that the Wii is better for the vast majority of people who enjoy playing games.







