I think the best thing they could possibly do is provide a wide swath of benchmarks for each machine sold. The user can quickly see if the machine will provide

I think the best thing they could possibly do is provide a wide swath of benchmarks for each machine sold. The user can quickly see if the machine will provide performance that they deem acceptable. Require it to be displayed in a standard format. The trouble is in getting unbiased results. I doubt Valve would want to test each model themselves.