That's what I got out of it, too, Mantidor. I don't think they had a clear purpose in mind when they sat down and wrote the article. As far as I know, I saw that when developers actually tried on the Cube, they could get a whole lot out of it, as much, or even greater than most high-end Xbox games. Heck, look at Pikmin. That many active AI's in such a beautiful environment didn't happen on the Xbox, as far as I recall. So really, if the Cube was nearly as powerful as the Xbox (or just as powerful when used properly), and the Wii is a good bit more powerful than the Cube, then of course the Wii is more powerful than the Xbox.
On a side note, I'm not surprised he was saying the Wii could produce games almost as powerful as the PS3 and 360. My current hypothesis is that regardless of actual capabilities, developers are only going to push graphics as far as they are expected to on a system-to-system basis. I don't think the Cube and Xbox ever really got used too their full strength last generation by anyone, because it's cheaper and more profitable for developers not to. I think the same is probably true to this gen too, only worse, because it will cost so much more cash monies to produce a game that really takes advantage of what any of the systems have to offer, including the Wii.