A few years ago, Apple used to make their own propriety CPUs for Macs. Does anyone remember that? Then they had the "brilliant" idea: "why are we competing against Intel" in CPU technology? That's a losing battle. So they dumped their own CPUs and started using the intel chip in Macs.
Canon is in a very similar situation right now. Nikon buys the best sensor from whereever they can find (Sony, Aptina, Renesas) and uses them in their own cameras, concentrating instead on the other aspects of a making a good camera (something that is Nikon's speciality).
Canon, on other hand, (just like Apple was against Intel), is stuck with "competing" in semiconductor technology against electronic companies like Sony (D800 sensor) Renesas (D3s sensor) and Aptina (Nikon 1 sensor). Good luck with that.
This is 100% guranteed a losing battle.
Canon should seriopusly consider this: when upgrading 7D, put the best sensor in it, even if you have to buy it from a third party.
Or stay at the bottom of dxomark for the next several decades ... What's the probability Canon will start beating Sony (who makes 30 million sensors a month) in semiconductor technology? Nill. I actually predict the gap would get even bigger in future.
But wait. Aren't the 5D mkiii's OTHER FEATURES (besides the sensor) it's major advantage over the D800?
So if Nikon just "slapped a sensor" into their camera, what exactly were they doing the whole time? I don't think the the D800 is groundbreaking in any way besides the sensor. Based on the OP's theory, shouldn't they have had more time to perfect an ergonomically brilliant, award winning piece of design? That camera looks squished & melty and exploding with buttons, ports & dials to me.
Canon already had a pretty great sensor in the 5Dii, why is it so wrong that they chose to focus on ALL the other aspects of photography & not the "film". IF photographers can't make a decent exposure from that sensor, well, there are bigger problems.