The Nintendo Wii is not an HD game console like the Xbox 360 or the PS3. It looks better on small analog televisions than giant flat screens. When asked if Nintendo was going to release an overdue HD Wii, Nintendo's Shigeru Miyamoto played it coy:

...Iā€™m afraid we cannot confirm what we are doing today. But the fact of the matter is that technology is evolving all the time and in Japan, for exampleā€¦ All the analog broadcast will be stopped and shifted into the digital broadcasting. So many things are taking place and we are working in terms of the changes of the technologies all the time.

Read into that what you like. Miyamoto Interview [3sat via Nintendo Everything via GoNintendo]