I'd hesitate to jump to the conclusion that Canon intentionally cut this functionality out of the camera in order to protect their business.
First, this functionality comes from grabbing frames from the Live View display buffer instead of the regular video mode, hence the odd 1.43:1 aspect ratio and resolution (side note: Andrew might like that for anamorphic work). Secondly, and perhaps most importantly to the matter of intent, this was found on the 5D Mk. II, Canon's first video-capable DSLR. Canon wasn't, at that time, expecting to completely flip the indie video market on its head -- they didn't even release the camera with 24p; I can't think that cutting 2040x1428 RAW capture via a display buffer was a matter of product tiering... not yet at least.
My guess is this: just as in general software development, Canon probably had people writing code for the camera's Live View display functionality. Perhaps as part of diagnostic testing or just general exploration, this function was written into the camera's firmware/OS. However, most likely due to the odd nature of the function and it not being planned as a feature from the start, no further development was done. The code associated with this functionality was probably subsequently disabled. If anyone's familiar with modders and hackers finding new levels. models, and features hidden within the code video games, I'd parallel this discovery with that. Also, considering the potential reliability issues, the extra time, testing, QA, cost of development, and the data rate limitations on both the camera and CF cards, implementing a feature like this in a camera like the 5D Mk. II just wouldn't have made sense at the time.
Of course, my guess is as good as any at this point. I certainly think Canon's been taking the piss on the market with its lacking developments in affordable large sensor video solutions, but I'm not sure this is directly related to that.