Some decline. When it's close to it's best year, month to month. Wii spent the better part of 2009 living off it's name, rather than games. Hard to imagine the solid lineup we know of thus far won't at the very least, keep sales steady.
Also, we know nothing of the second half of the year. What we do know, is AAA games from Nintendo themselves a releasing in the first to mid-part of the year. And more than just one game. This is unheard of. Nintendo's way of saying sorry for 2009? Whatever the reason, it's a welcome change. But are we to believe that they'll have nothing left for the end of the year, when Move and Natal are set to launch? This late in the game, I doubt they'll respond with another hardware add on. So it must be software. This is the company that launched MM to help combat the launch of PS2. And I'm sure they'll use a big name title (Or titles) to do the same this time.