Nintendo doesn't have an excuse this time. With Microsoft adjusting their price for the base XBox 360 to under $200.00, not having the Wii in stock will just allow room for people to purchase the Microsoft alternative.
We can assume Nintendo was playing it safe with the supply issue, but after so many months of being sold out people just get tired of waiting....
Actually it's understandable that Nintendo couldn't keep up given the demand of the thing. It's the leading console on the market surpassing even the 360 in a very short time. Now I know some of you will argue that Nintendo could keep building factories but it doesn't work that way. Many startup companies have collapsed following that scheme because what happens is the market begins to oversaturate and you never recover the cost of building more production. At this point the market is starting to saturate so demand is falling. This is probably the biggest reason why it is back in stock. I think no one, not even Nintendo thought this platform would be such an amazing success.
While I don't think they faked shortages since it would accomplish nothing except make them lose out on potential sales, it boggles my mind that they couldn't solve the supply issues sooner. I don't care how popular the system was.
Considering the demand and the way Japanese manufacturing uses lean production with extensive in-house quality assurance measure, their shortage can be justified. Every Wii they've built has been guaranteed profit - they are playing it smart. Building more factories to produce decreases profit due to fixed costs. Sure it may help ease the inventory stock, but that's probably not what they were going for.