Looks like B&H and Adorama have already applied the new pricing to the preorders. For anyone seriously considering one of the superteles, Amazon will still let you preorder it for the old prices, e.g. $1000 less for the 500mm f/4L IS II. If you preorder that lens now, and receive it in December, locking up that $9500 compared to the new $10.5K price means a 10.5% ROI and a 25% annualized ROI - try earning that on another investment...
I'm wondering about your statement. Does amazon really say this?
I've found that Amazon does not lock in prices. They have cancelled my pre-orders in the past when prices increased, so that after waiting in line for a new camera for months, I had to re-order and go to the back of the line. Naturally, I did not, I went to Adorama instead for the re-order.
amazon does not seem to do this right away, so they may cancel your orders anytime, right up to the day before processing your order.