Hrm. I see some people over at Hardforum asking why water temps matter. I can't address that there, but I have a soapbox here
Let's think about this.
If the water temperature isnt controlled, and performance is published ONLY as CPU temperature, then it is possible for a block with worse performance to be ranked as the top performer. Far better to publish Delta T (Die temp - water temp). The block that can get the CPU temperature closest to the water temp is the best. That seems pretty straightforward.
What is not so straightforward is the interaction between flow rate and performance. Blocks that are more restrictive will affect the performance of the radiator as well. So the water temp is shifting, the room temp is probably shifting, and the flow rate is different in every setup.
That testing is not especially useful then, unless you happen to have EXACTLY that same setup. And even if you do, it doesn't help you get any closer to optimizing said setup.