This all about our priorities not "what canon/nikon could do" and about our personal standards in of image quality. It is funny that we'd call 36MP unpractical and then turn and pretend ISO51K is practical and suddently everybody is shooting at night. Practical for who?. Low light is often, crappy light and I'd much rather have GOOD controlled beautiful soft light than crappy light whenever I can get it. As many have said, this isn't "dark-tography" it is photography. Therefore as admirable as the 5DmkIII, or even teh superior D4 and 1DX look on paper, the reality is that just as you question the need for 36 or 50MP, one may question the need to shoot at ISO 52K. The number of people that NEED that high ISO is likely as many as those that NEED 36MP. I think both cameras have different people in mind but just as focusing on resolution is not the best way to evaluate a camera, focusing on low light isn't any better. This post by Canon+Nikon shooter Scott Bourne puts it very elegantlyhttp://photofocus.com/2012/03/27/photographic-religions-the-religion-of-low-light/
However, I do see many that desire to have that safely net of being able to shoot at really high ISOs regardless and those that wish for that unparalleled resolution of the D800. Who's to say they are wrong?. But the point of versatility isn't as black and white as you paint it. The fact you have the option to resample down to 22MP is in fact versatility and practicality at work. Many argued the 5DmII was more versatile and practical than the D700 because it could:
-downscale to control noise
-when noise wasn't a problem, you got 21MP worth of detail.
-increased cropping flexibility.
-4 fps was plenty for most people (vs 8fps on the D800)
Were they wrong? I don't think so and I think this applies to the D800 today. So I just don't see 36MP being an issue in any way and in fact IS a plus for versatility and practicality given the image quality so far has been praised even by pixel peepers: http://diglloyd.com/
Ultimately, as much as I'd have like to see canon have the best overall camera, I think for the majority of people, it really isn't any better than the D800 and in fact image quality wise, it will often be behind. HOWEVER, I'll 100% agree with those that have said that SPEED is their priority and why they justify the 5DIII that way. How many people actually NEED 6fps or even 8fps (D700) or even upwards of 10fps with the D4/1DX? I think that minority crowd is already well served.
Let's not kid ourselves. I think once canon makes their own 30-40MP body (and it WILL HAPPEN), big resolution will once again magically become "practical" and all the arguments for the D800 will apply equally. Thank Nikon for showing how much a 36MP sensor could kick ass and all but made the naysayers eat crow in large quantities. Daring steps like these that distrupt the market is good for everybody and Nikon should be praised since it means others, including Canon, will follow.
To be fair, both sides have switched ideologies. All of the sudden the Nikon guys are all about the megapixels, and the Canon guys are all about low-light performance
Exactly. I've said it before, 36MP in 2012 is the "21MP of 2008". 21MP was the state of the art a few years ago. that has changed. Technology simply advanced and we're flying higher now. But to be fair, it could have been really crappy 36MP. I think what has caused the resurgence of BIG MP = win is simply the fact the sensor is really really good.