Can't comment on the Mark III, only used the Mark II. Also, disclaimer: I'm shooting Nikon now.
I see the argument that dynamic range doesn't matter, or only matters in edge cases quite often. Well, I guess there is some truth in it. It depends on your work/interests, lots of conditions. DR may or may not be important to you. Instead of going back-and-forth with academic debates, I'll show how it helps in various situations I shoot in - with examples.
I shot the International Pillow Fight Day event here in Saigon. Fun work, for free of course (non-profit, fun-loving people organized it, couldn't resist). The event took place at 3pm, very hard light, in park where the trees didn't offer enough coverage. Yeah, high contrast situation, hard like, dark shadoes, bright patches of sunlight. Now not all photos are like that, but there are quite a few where I pulled at least 1 stop from the shadows without loss of detail, without smudging the colours, and without any visible noise even at 100%. That's what dynamic range is in practice.
It may or may not matter to you, it matters to me and probably the people I did it for too. I wouldn't be able to do it without the DR of the d7000. Here: Pillow Fight Day Saigon 2012
Now I don't do many events, I'm an interiour photographer, doing lots of landscapes as a passion (and these year, more and more people, fashion, portraits). In interiour photography, good DR is gold. Ironically, some of the most expensive properties I shot had the worst lighting. Huge rooms, big windows, shooting scheduled for 3pm (and no, I couldn't change it). Hard light coming through windows, rooms too big while lighting not enough to overpower the natural light. This is situation where it's impossible to get a perfect exposure, and HDR is out of question with apartments (too long to explain why). Examples starting here, and the next few pictures: http://molnarcs.500px.com/apartments_villas/photo/16
Landscapes. I don't think I have to explain this one, because its kinda obvious. That said, 90% of my recent landscapes are less than 10 EV, lots of good shots that require minimal post-processing - and in many of them you wouldn't see a difference even if your camera were limited to 8 EV. But that 10% - I'm glad that I had some EV leeway there!
Remember, good DR doesn't mean pulling 6 EVs from shadows. It means pulling 1 EV cleanly
- or even half EV. The more DR your camera has the better in the situations above.
Lastly, in commercial photography, there is a good reason top PROs use Hasselblad and medium format cameras. They have phenomenal EV at base ISO, and they are using every single bit of it. Walk through any upscale shopping centre, and you'll see tons of large backlit prints - and it's not just resolution and megapixels. Here's a video comparing the d800 with a Hasselblad. The new "king" of DR in 35mm format can't stand a chance (and why DR does matter in commercial photography). D800 vs Medium Format with Roth and Ramberg
RichATL, you're wrong on so many levels that I lost count. DR does matter in quite a lot of situations. Now you may or may not shoot in those situations, but saying that only brainwashed "pixel peepers and gearheads" care is a bit over the top. And as to your jpeg argument... ever heard of picture controls? Seeing your "computer programmer in Japan" line I guess not.
Ultimately, everybody has to decide for himself. If you rarely find yourself in a situation where you'd love to brighten the shadows up just a bit more, but you're losing details... I guess it doesn't matter. Sports, indoor events come to mind with constant, even light. Lots of examples where DR doesn't matter that much. That said, it would still be prudent to make your voice heard to Canon instead of going full denial RichATL. Higher DR has tangible, very practical benefits in many situations. Is the gap Canon and Nikon/Sony sensors huge? I honestly don't know. It's there, and its not good in my opinion.