D&M seems to be pretty conservative in general; however, there are some cases where they deliberately down rate a component.
For example the amp section of the SR-6001 and the SR-7001 were independently measured as identical, but the SR-6001 was rated at 10 Watts less. From a production standpoint, it was less costly to mass produce the SR-7001 amp and use it in the SR-6001 than to produce a slightly weaker amp design. From a marketing stand point, they wanted the SR-7001 to look like a better amp section the SR-6001. i don't know if this is still true of the 6000 vs 7000 series.
Additionally, it is unclear if the S&V measurements are full bandwidth (as specified by Denon) or only at 1kHz. Here is their description of their measurement technique:
http://www.soundandvision.com/bootcamp/53#WXCmUVVFVmzpLq8k.97
Based on the following blurb, I would assume 1kHz unless someone corrects me:
Since they refer to the signal as a sine wave, I would infer a single frequency, but I am getting out of my comfort zone and hope someone like Peng can confirm or correct me.