I guess when the D200 came out with its professional quality body, weather sealing etc., Canon was caught on the wrong foot.
Typically, when developing a new product, companies have more than one version of the product available, one of which will become the final product. I bet Canon had a "weather sealed" version without built-in flash, a weather-sealed version with built-in flash and the current version. During the final review with the bean-counters, they decided to finalize the non-weather sealed version without the built-in flash, correctly surmising that the "full-frame" would sell the product.
Nikon also probably had a few versions on the table and after Canon announced their final version, they quickly put their D200 "weather-sealed" version with built-in flash at an attractive pricepoint, and then made final adjustments to the manufacturing line, accordingly.
Now Canon has to suitably reply when they come out with the 20D replacement. Since the 5D has come out with the "weaker" non-weather sealed format, the 20D replacement cannot one-up it on that score.
So based on the above, the only way Canon can grab the spotlight back, would be to put a 35mm sized sensor in the 20D replacement, with around 10.4MP resolution and the pixel pitch of the 5D and the built-in flash but without weather-sealing etc. Leave the cropped-sensors to the "Digital Rebel" arena. At a pricepoint of around $1900-2100, it would sell very well. But that will cannibalize sales from the 5D, I would suppose.
Just a conjecture...