There should be a way to delete orders from the 'canceled' tab - sometimes an import doesn't go quite right, or perhaps you created the order to get a shipping cost for a customer who backed out - there's no reason to keep all that data in the canceled tab.
Furthermore, and more importantly - if it's a botched import - you have to change to all new order #'s or re-importing will only update the already botched orders (and if it's the order # that's botched, you're way out of luck.)
Let us delete canceled orders.