This, they test this way to show us, the consumers, what real world differences we are going to see at resolutions that we play at. Yes, we all know lowering the resolution will exaggerate the differences in cpu power and clearly outline which cpu has the most raw grunt, but what good is it if at 1080p the difference between cpu a and cpu b is 1 fps. This is what you need to understand.
If you play at 800x600 then sure that would be more valid.
If you want to have a high end gaming ring you change video cards every year, but you don't do the same for the CPU. So when you buy one you want to be sure you get the most power for your money. So this is why it's important to review a CPU on lower resolution or triple SLI setups, so you have a clear idea about the CPU power you are going to buy.