Canon production lines have limited capacity, they do not just throw up a new facility in order to keep a older model in production.
They likely have a very large inventory of older models right now, based on the FY2011 annual report, inventory is pretty high. So I expect all of their production capacity that was devoted to the 1 Series and the 5D series is churning out the new models, and will be running at capacity for the next year or more. There is much more profit in the new models, so they will try to produce as many as possible. Even so, there will be many waiting to get the new models, they just will not be able to make them fast enough for the first year.