Thinking about it i don't believe its a manufactured shortage. For the most part nintendo has to make systems no only for the US but all other regions to. Spreading out each batch across the regions like that would make it seem like a larger shortage than there is.
If I remember correctly, Nintendo ships Wii's by boat instead of plane to the US to cut down in shipping costs. My memory is foggy so i could be wrong but i believe i had gotten that info from a Nintendo rep when i was working at GS. Take that state meant with a grain of salt.