The point is, ther are a significant number of phtographers who regularly shoot above ISO 400, even in daylight hours. DxO scores don't take this into account properly.
What photographers spend their time shooting is irrelevant so far as DxO scores are concerned.
I aim to shoot such that I get the best image possible at all times. That necessitates keeping the ISO as low as possible.
DxO aren't reviewing cameras, they're measuring sensor performance.
Yes the D800 would benefit me as a landscape photographer, but I don't have a need to print larger than A3 most of the time
The benefit of the increased DR from the D800 is not relevant to the size of printing - megapixels is.
To be perfectly frank, impact sells more images than the dynamic range of a camera. You can use any camera from a fairly basic poimt and shoot to the most expensive large format camera to achieve impact, so the tool used becomes an irrelevance.
Right. If the subject material is poor then a camera with a better sensor won't make the photograph magically better. But on the other hand, a camera with a better sensor in the hands of someone that knows how to use it will result in a better image than they would be able to achieve with a weaker sensor.
DxO measure one aspect of the camera - the sensor performance.
When making a decision about which camera to buy, there are factors other than how the sensor performs to take into consideration. When we walk into a camera store and pick up a DSLR, we have a chance to hold it, feel it, evaluate all of the ergonomic aspects. When we're in said store, it is beyond our ability to measure sensor performance then and there. DxO empowers us by delivering to us measurements of camera sensors so that when we walk into a store to evaluate a camera to buy, we can make a decision about what's on the outside and on the inside.