Volohk’s explanation for this phenomenon, that some groups are more likely to respond than others, is certainly plausible. However, an even more likely explanation is simple random chance. Unless this trend manifests itself in a lot of polls, it’s almost certainly just random variation. For one thing, the confidence interval of these things is usually at the .05 level*, which means that one in twenty times, the whole poll is bunk. For another, unless there is some serious work to stratify the sample–which there usually isn’t in these polls–the chances that the demographics of any particular poll will match up precisely with the population as a whole are not very high. And that’s even more true of comparatively small groups like American Jews. You’d be much unlikely to find a poll that has, for example, twice the number of Baptists as their actual percentage in society.
*See comments below for discussion of this terminology.