users of these sites, including DXO should be aware that they do NOT test lenses, and do not have equipment capable of testing lenses.
What the sites do test is a lens / camera combination. What this means to those who read the results carefully, and they tell you this, is that the results only apply to a lens used on that exact camera model and not on others.
Very true, Photozone also points out that it's results are not comparible across different systems. Whilst I'm aware that a 18MP sensor is more likely to show a lens' limitations than an 8MP sensor, I'm always intrigued that some 'lens test' results are so poor compared to others. For example, the EF 85mm f1.8 comes out looking quite poor in the SLR Gear sharpness (sic) test, but better in the Photozone test (Photozone seem to have got a better copy when they re-tested this lens at 15MP). Perhaps it has more to do with where each reviewer sets their 'scales' in terms of what is excellent, good, acceptable and poor.
I guess the advantage of the The Digital Picture's ISO12233 chart crops is that you can see for yourself what each lens' results look like, but even then they are only tested at one distance.
Finally, I have to agree with kubelik; there is indeed more to a lens than its resolving power, unfortunately I have learnt this through bitter experience!