I find this very odd. DXO goes in lengths to determine all other attributes, but not resolution? Why's that?
DxO's lens benchmarks cover what you are looking for. It is not practical to test a sensor's effective resolution without a lens. And once you use a lens to focus a test image, you are measuring the performance of the lens/filter/sensor/processing combination. Meaning you will get significantly different results for different lenses.
I'd think now with all this 20mp this 30mp that, it'd be interesting to see how much "real" resolution those high mp camera do really offer? I mean just take an example of Canon 7D, it really doesn't offer 18mp resolution with its horrendous AA filter.
Same answer. You should be able to tell the difference between e.g. different sensors by comparing how well they perform on the lens benchmark using the same (highest quality you can find) lens. That would likely be something around the 100mm (e.g. 85mm portrait, 100mm macro, the newer 70-200 f/2.8...).