I think Nintendo is playing coy on both price and release date so that Sony and Microsoft can't react much. Right now, for instance, Microsoft probably feels very comfortable with it's price point, being at least $100 cheaper than PS3. If Nintendo announces Wii @ $200, that's a little bit scary. Nintendo may also be considering bundles. If these controllers aren't cheap (they certainly pack a lot of technology in) then Nintendo may want to bundle two or even more with the system so players don't need to spend another $150+ making their Wii multiplayer.
Oh yeah, and the date. I think if Nintendo's smart, it will try to lead Sony into the market, but it probably wants to do so late in the year (well obviously, they said fourth quarter). Not saying when it will launch until Sony commits to a date would let Nintendo give itself a slight advantage.