While the 'math' is the same, political polls are inherently far more political. We'd see more parallels if say the Steam survey (and others) were being influenced by the vendors of said products to some end. It seems none of the major vendors really have a reason to do this, unlike in politics where all coverage increases or decreases public awareness, so bad news is still free coverage. Also, I recommend we drop the political parallel discussion as this isn't the Soapbox .
Biggest difference.
Valve samples actual facts about the HW.
Phone polling collects peoples opinions of the moment, and they might not even be true opinions.