Polls are biased. Its like polling Bammers on if the Vols would win a National Championship, your not gonna get a fair response. This is the reason the American people believe that Bush is a horrible president, because of these biased polls. If you really want to see if the American people favor the war and the president then poll us all. Still even then you are gonna have people that have NO political background giving answers and that right there is still a reason to believe that polls are biased. So I guess basically, polls are biased based on ignorance.
These polls are a statistical sample with a margin of error usually around 3-5%. They usually involve a sample size of a thousand of people or more. IMO its more accurate then you believe.