Someone could be smart and defer doing the survey and even do it on another person's ultra-high end rig using their steam password . Or just throw some stuff that they have lying around into the rig and turn up the AA etc to unplayable settings , Valve would be none the wiser .
Well until they see a 128 mb FX5200 running at 1600X1200 with 6XAA , 16XAF and all of the possible goodies turned on .
How many people would care enough about a stupid survey to bother with all that, two?