The strength of the DxO Mark method and similar methods is that it allows for accurate characterization of a sensor and/or optical system.
The weakness of the method is that final image quality (e.g., what is seen in a print or on a display, such as in a web gallery) depends on much more than raw-level characterization.
For example, a raw-level characterization may show more promise for the Panasonic DMC-LX3's sensor compared to a Canon PowerShot G10's sensor, but raw files rendered using these makers' respective software (SilkyPix and Digital Photo Professional) may yield opposite results. This may seem initially like a bogus comparison because different software products are being used, but on the other hand it's a common scenario that will apply to many users (i.e., owners of these two cameras will simply use the software that comes with the camera).
This is the classic tradeoff of the scientific method. By isolating specific variables, you can get a very good understanding of that variable within a limited context. The downside is that it's insufficient to explain the big picture or the broader context, without a (much more difficult and time-consuming) examination of the whole context. For example, we have detailed models of the human eye, which can explain certain visual phenomena but is insufficient to model color appearance. As another example, there has been much study of the individual contributions of various nutrients (vitamin B, antioxidants, etc.) to health, which unfortunately are poor predictors in general because they do not take into account the much larger complex system (i.e., how all of these elements interact).
Don't get me wrong. I applaud DxO for their efforts in launching this site and for making the (summarized) data available. It is certainly the right way to go when developing raw conversion software. But if you don't develop raw conversion software, and you're just a good ol' photographer, you have to ask yourself if the numbers/data are going to be relevant to your workflow. Or, put another way, if the doctor tells you to eat fewer eggs because lower cholesterol means a smaller chance of a heart attack, you should ask if that is really the factor that matters.