You can make the argument that better DR may make your life easier.
I don't mean to sound elitist, but this isn't something to be taken lightly. If you're taking photos for fun, I can see how spending 1 minute in post production to extend the DR of an image vs. spending 10 minutes isn't a big deal. However, if you're working on a tight deadline, need to process six dozen images to present to a client, and your livelihood depends on the quality of your images, out-of-camera files that "make your life easier" in post production isn't a luxury, it's a necessity.
Obviously, this doesn't only apply to DR, but also noise, sharpness, color reproduction, contrast, etc. It all adds up, and any time you can save in post production is time you can be spending behind the lens and making more money. I don't know about you, but I'd rather be shooting than staring into a computer screen and fiddling with a mouse
If you regularly find yourself dragging up the shadows, then you might as well jump ship and head over to Nikon where the grass is greener. Or you could ETTR, utilize the sensor DR better (Canon does seem to have a bit more highlight headroom than Nikon by about 1/2 a stop based on DPR charts), and correct exposure at the click of a button in post
I would certainly hope that anyone attempting to earn a living with Canon gear utilizes a technique as simple as ETTR
Like you said, Canon files are incredibly good at highlight recovery, which makes ETTR a very useful tool in extending DR. My point is that over time, everyone is going to learn tricks like ETTR, or something as basic as using reflectors, fill light, multiple exposures, etc to extend DR. You're going to do that regardless of whether you shoot Canon or Nikon. Ultimately, however, a file with more latitude right "out of the box" will help you create the best image possible.
I'm not quite sure how this thread turned into a talk about DR, but DR is just one of MANY factors that determine IQ. Even if the D800 proves to have better DR than the 5DIII in the real world, I can just as easily decide that I hate it due to color reproduction, contrast, and sharpness that aren't my cup of tea. I remember the first shoot I did with the 5DC. I was blown away by the film-like image quality of the files. It was like I was shooting color slides again, and the color, contrast, and sharpness were simply stunning. I'd never seen such incredible IQ on any digital camera before. I didn't care how its DR or ISO measured on some on chart posted by some geek on the internet. The images just had that certain look and feel to them that I cherished, and at the end of the day, that's all that mattered. IMHO, that's why you have to try these things out in the real world before determining a winner.