When nikon announced the new D800, you could pre order it from the next day
canon sucks on that part...
You can also preorder Canon as soon as they are officially announced. I had an 800E on pre-order. There was no difference between Canon & Nikon on the 800 and 800E.
The Canon T4i shipped less than 1 week after it was announced. It was officially announced on Friday, June 8. I had it in my hands one week later, on Friday, June 15.
Nikon actually had more disruption of manufacturing because of the incidents in japan and elsewhere, with many items out of stock and in short supply.
Really no difference overall. Canon is making sure the product performs prior to shipping.