Of course there are "product cycles" as in they are working on something new that we call "5D3" and that they started working on that some 3-4 years ago. Canon probably already have a few team prototyping different versions of the next "1DX2".
Then, when it comes to releasing a product and marketing that specific department will run the show and play the waiting game, getting most bang for the buck game etc...
I think photo industry works the same as many other industries, say cars for instance. Developing a "new car" as in a totally new model takes 10 years. And that model will "live" / have a value for about ten more years. Of course you do small updates yearly, perhaps an enginge from a parallell model, interior design... (which is common started 2 years in advance). But then the model is oudated and replaced with a new one they worked on those ten years.... repeat.
I think the same goes for photo (although shorter cycles perhaps).
The 1DX came out as a new platform (ie they stoped the 10 year old earlier platform and started a new)
What they will do with the xxxD, xxD, 7D and 5D only they can tell.
But surely they talk about it in terms of product cycles.