A sample size of 1,000/>300,000,000 certainly doesn't make for a strong argument regarding the feelings of the total population, and certainly shouldn't lead anyone to conclude that 9/10 Americans believe in God AND are religious.
Surveys are terribly unreliable, they attract more people who will answer in the affirmative to the questions posed. Plus, as therblig points out … they tend to bring out the liars in people.
Also, they were only given the option of yes and no, which probably skews the numbers towards “belief in God,” because people on the fence would be more likely to go with what they viewed the as the “right” (as dictated by societal norms) answer to be. I believe in God (but am not religious, more spiritual), but I hate when surveys, polls, and what not are blown out of proportion. Based on my observations of society, and the church parking lot across the street, people were totally bluffing on that survey. I also have to wonder how close this was posted to the rapture, and if people were like… “well, just in case.”