I read about it back in September, it basically means Amazon is selling them, but not them directly.
Like, Amazon UK, when looking at a 3DS, you get this message
In stock.
Dispatched from and sold by Amazon.co.uk. Gift-wrap available.
Which is the case in the page I looked at, sans one, the aqua blue.
When looking on Amazon US however...
In Stock.
Sold by (insert company here) and Fulfilled by Amazon. Gift-wrap available.
Which is the case in the 2 pages of 3DSes I've looked at, no exceptions.
Same goes for the Wii U, Amazon UK sell it directly, Amazon US sell it through someone else.