I see what you mean in that the same games as on the other 2 won't be released on the Wii because the hardware just can't handle it. This is fine.
However this really should not be a problem in itself for the Wii. In other industries suppliers usually adapt to the major market players even when they need to design more basic products. Take the Korean car manufacturers for example. We don't see them having shortages of features like gas tanks or cup holders because Toyota, Honda and Renault have higher quality requirements than they do. Why is this such an issue in the console market? Why can't the software designers make custom software for the Wii when they know they'd have a good chance of selling millions of copies?