Remember, they *did* increase the production once already, from 1.2 million units/month to 1.8 million units/month. That may not sound like a lot, but that's a 50% increase. We're talking about producing the same amount of units as Microsoft has in half the time. This, of course, is in addition to the large amounts of DS Lites they're churning out (in record numbers, apparently).
Is Nintendo milking the "shortage"? Possibly. But the fact remains, they're shipping (and, of course, selling) more Wiis that just about any other system *ever*.