I agree, I think it's hard to say there are shortages when Wii sales numbers average out to be over $1 million per month since it's release in November.
Demand is just insane. That's all there is to it.
Regarding the transportation methods, shipping by boat makes perfect sense. As another forum member mentioned, transportation is not the problem. It's the amount of systems that Nintendo can manufacture and the incredible demand for the system. It doesn't make any sense for Nintendo, as a business that wants to make as much profit as possible, would want to use a more expensive method of shipping (by plane) when there is literally no need for it. It's like "Hey Nintendo, do you want to spend more money on shipping or reduce your expenses and make more profit by shipping via boat?" ... It's really a no-brainer.
Just to put the demand in perspective, I work in retail that sells electronics (games). And day in and day out we get so many calls asking if we have any Wii's in. When we do get them in, they sell immediately. Recently we actually got a decently large shipment of 15. It took us less than 24 hours to sell through all of them (and considering we were probably closed for at least 10 of those hours, that's pretty incredible.
To put that in perspective, we'll probably sell one to two PS3 / 360s in a week's time.
As far as how long it'll be before you can just casually walk into a store and buy one. I have no idea. When the system first came out, I figured it'd probably be around mid-to-late January before you'd be able to pick one up. I figured it was all Christmas hype. But meanwhile, while 360 and PS3 sales have slowed down after Christmas. The Wii continues to sell at an incredible pace. One might not be able to casually walk in and get a Wii until sometime during the summer. If it doesn't happen then, then don't expect to be able to walk in and buy a Wii on any day until sometime in 2008.
If that does occur and the demand is this constant throughout all of 2007, then there's absolutely no question in my mind that Nintendo and the Wii will easily surpass the 360 in total sales numbers by the end of the year.