Actually, I saw a quote from one of the web sites from Canon, saying that they were caught by surprise at the sales volume. They also mention their suprise on their web site at the initial demand.
Even now, many camera sellers can not get enough for the Christmas demand and sell out in a few days after getting stock. I'm sure that they will all have them in stock after the holidays.
As to those saying that a company restricts production to increase demand, this is silly. Demand for the cameras was so strong as soon as they were announced that some sellers stopped taking pre-orders because they had so many that they knew they could not fill them all.
The reason for shortages is simple, the sales department projects sales, components are ordered, and production of lot sizes to meet sales projections begins. Some parts are just in time delivered, but I have found that small cheap components are usually run off in large batches by subcontractors, and just held in inventory for just in time shipment to the manufacturer. If demand outstrips the production capability, there will be shortages, but the factory may be able to increase production rates a little due to the parts held in inventory by subcontractors. However, if the demand far outstrips the provisioning of components, then long lead components become a big problem. The production of the 21mp sensors is limited to factory time allocated, silicon wafer availibity, and production capacity of the actual machinery. They are undoubtedly made in batches, so there may not be a window open for another batch, and it requires replanning, acquisition of more raw materials, etc to speed up production.
I have over 30 years experience in product manufacturing, and every company I've delt with faces the same issues. You can not just simply increase production overnight.
The same applies to overproduction, it is usually less expensive to continue to overproduce for a limited time than to slow down or shut down a product assembly line.
You did not see this with the 60D.