I agree, I've never heard of any other product being this popular and in this short of demand, its their financial guys figuring they can make a profit by cutting the retailer supply and hiking up each unit price, simple supply and demand, and at the moment theirs a massive demand!
Lets see 6 months to a year from now when the PS3 is established, you'll see the wii price really drop!
Nintendo aren't the ones pushing the price up.
As for manufacturing, as I understand it Nintendo work very closely with mainly one or two companies to manufacture their hardware and have done for years (Panasonic is one iirc), which possibly ties their hands a bit in regards to ramping up production beyond a certain limit, but also helps ensure quality is good (when you've got a manufacturer who has worked with you for years, there is slightly more incentive to do things properly than using companies who might only work with you for 6-12 months).
It's also a fairly major investment to increase production line capacity beyond a certain level, and whilst it's certainly possible you risk spending out very large amounts of money for something that isn't needed a few months later (if you look at Sony's financial records for example, they have huge liabilities/amounts of money tied up in factories that if they aren't very careful might end up sitting idle).
There is also the question of sourcing additional parts - there is a finite amount of manufacturing capability in the world able to produce things like the graphics chips, cpu's and memory used in a games console and getting additional supplies of those (on top of what you've already planned for) can require a lead time of months, unless you are willing to pay a hefty premium for them*.
IIRC Apple for example tied themselves into a fairly big long term contract with Samsung to effectively get first dibs on any flash memory chips made by them for several years, and multiple million units - it meant that Apple got a guaranteed supply of them (before anyone else would get a look in), but were committed to buying a huge number parts that might have ended up not being of any use (Apple gambled on the Nano taking off, if it had not they could have been left with millions of pounds worth of flash memory).
I guess what i'm saying is, that depending on the manufacturing strategy employed by the company it can be possible to ramp up production massively, but it depends a lot on how much they value quality control, their relationship with suppliers, and how much they want to risk - Nintendo generally outsource production to trusted long term partners, Sony do much of it in house, MS outsource everything to third parties who may only be on short term, lowest cost contracts (this is all from memory).
Each method has it's advantages and disadvantages.
*Sony's problems with the laser used in the PS3 is anything but unexpected (it was a new part being made by one or two specialist companies), there was a similar problem with a relatively small and (normally) cheap chip used in DVD/CD players a few years back, caused by the boom in mobile phones (which used the same chip), that was a worldwide problem for a simple chip, and that took something like 6-12 months for production to ramp up to meet demand (think about it for a second, that was a single part, not a device comprising of hundreds of parts, any one of which might cause a delay).