Some people shoot 9 images per HDR depending on the range of light in the scene. That's 675MB of a memory card used; that applies to hard drives as well for those who don't delete their original files. Also, just because your end product came out to 2XX MB does not have any bearing whatsoever on the results others might experience with a different workflow and different number of shots.
Well you said the HDR file would be 500MB this is plain wrong and no matter if its 9exp or 3 exp the output file will typically be about the same size.
Also thats if someone is shooting uncompressed RAW which is 70MB. I believe most including myself will shoot lossles compressed which comes in around 40MB. Add in that the extra DR of the D800 and most will no longer need 9 exps. I would shoot a ton of 9 exp HDRs with the D700 but now with the D800 I likely will stick to 5 max. The DR of this camera is incredible
If your going to make a statement like that you shouldn't cherry pick the worse case scenario. Break it down for people so they don't get the wrong idea