Sorry, Andy, if you read the end of the story, Gallup generally does release a summary of their methodology, which they did in this case. The reason why Gallup shows higher support for Obama than other polls is because they don't limit their respondents to registered voters, let alone likely voters. Instead, they interview anyone who answers the phone who claims to be 18 years or older. Heck, they even include aliens in most of their surveys.
The entire survey of Jewish respondents was 512 people, which to me implies a considerably larger margin of error than 7%.
I can tell you that there is a formula used in statistics where one can determine the margin of error to a specified probability (say 95%), based entirely on two variables which are plugged into that formula: the number of items sampled (in this case, 512 Jewish respondents) and the number of items in the total "universe" (in this case, the total number of Jewish Americans 18 and over, which is roughly 4 million). 7% happens to be a high margin of error for any national political poll, BTW. To lower the margin of error, they had to reach more Jewish Americans, but they probably decided not to because of the expense involved.
...the likely geographic concentration of those who answered the poll.
The Jews surveyed by their method would probably not have a geographic concentration much different than the general geographic distribution of Jews in the US. I don't see that as a particular problem of this methodology. But it's possible that the Orthodox and and more recently arrived Russian Jews - who tend to vote Republican in presidential elections and strongly anti-Obama - may have been undersampled because of cultural and language differences.