Here are the problems as I see them. First, DPReview does not consistently apply a noise threshold. So when a DR test hits the 2% luminance threshold before it hits the noise threshold, there is actually more DR available from the sensor and JPEG image and you can actually use it if you bring the in-camera JPEG into Photoshop. In these cases, the reader doesn't get a DR test from DPReview. The reader gets a nice accurate report on the camera's tone curve instead. If the test hits the noise threshold and that is used as the cuttoff point instead, you do have a somewhat reasonable standard of comparison. But that only seems to happen on the high ISO tests, and you have to look carefully at the graphs to determine which tests hit a noise threshold and which ones don't. The noise threshold is a "standard" that isn't always applied. Probably all of the DSLR based lower ISO tests are under-reporting the actual DR because they all hit a tone curve dictated luminance threshold before they hit the noise threshold.
If you want a good indication of DR, you should develop the camera's raw files using no sharpening, no noise reduction, and preferably no gamma correction. Then you can analyze the image using a program that will measure the response and measure the noise. There is no need to concern yourself with luminance levels as a threshold. Those values are completely manipulatable. Testing using a basic linear develope raw like this isn't a perfect solution. [8-13-2010 - A better test is to use the raw data without demosaicing it. In such a test you would simply test only red, blue or green pixels and they would have no processing at all.] Everybody doesn't have the same idea of what is or isn't an acceptable level of noise. Furthermore, noise that measures the same doesn't always look the same. But doing DR tests this way will be far better and have far fewer variables than anything being done by online review sites right now [8-13-2010 - with the possible exception of dxomark testing]. What we have now is a jumbled mess of sorta-sometimes-maybe-right test results.