Go back to sleep..
"I think I know what the 3DS looks like ... I actually had a dream about this ... it makes no sense ... I was a little disappointed ... whether it uses CD's or cartridges"
They are all pieces of evidence that you're not thinking straight/this isn't real, dreams aren't real you see.. Hell I had a dream about a month ago that the 3DS was a deep purple colour with glistening bit in it (like the Gameboy Color carts for Pokemon gold and Silver) and it actually had three screens (two normal DS size and one ultra widescreen, really thin one in between them) it had a double hinge mechanism so that all 3 screens lined up and that was the real reason behind the 3 in 3DS.
Tell you what a dream is: During REM sleep there are random firings of neurons from the back half of your brain during the creation of long term memories. The neurons in the front half of your brain don't know what to do with these signals and try to create a logical sequence with them.
I'm only stating all this because you seem to be shaping your ideas of the 3DS on a dream, which seems a bit ... well anyway ...
Other than that, I wouldn't be at all surprised if the design you dreamed about was very close to the one show at E3, as it is as good a guess as any when it comes to Nintendo hardware.
