That analogy would only be valid if people drove their corvettes in real life with S rated tires for the most part. AtenRa's testing represents how I think most gamers actually use their PC. It isn't isolating just the CPU if it's GPU limited, I get that, you are right. But I think most people actually game at mostly GPU limited settings.
A GPU bottleneck causing unusable FPS can be fixed easily by changing resolution/detail settings.
Also, people upgrade GPUs more often than CPUs. If a rig has sufficient CPU to be GPU limited that means it will be a good candidate for a GPU upgrade. When the new 14/16nm GPUs come out soon it will trigger an upgrade cycle and I predict we will see a lot of people will find themselves with GPU heavy/cpu light rigs.
In other words the maximum potential of CPUs does matter, even for people who don't buy top end GPUs.