It could be due to volume and manpower ratio. Someone earlier last year said that Delhi office was hiring local IOs. Perhaps other visa offices weren't hiring as much or at all.
It could also be due to quotas. Someone from the forum recently said that they got a letter from Buffalo to say their application was approved but to only send in the passport after Jan 1st 2010. This to me, suggests some quota issues.
Also from the forum, I got the impression that most other visa offices are processing post Nov-applications at a great rate but not Feb-Nov applications. Whereas, Buffalo was processing Feb-Nov applications before Post-Nov applications as suggested by trackitt. So for post-Nov applicants this looks like it is taking a long time at least at Buffalo. Someone once said that Buffalo has given out more PRs than other visa offices last year. They were just not from post-Nov applicants. I don't know how true or false that is.
Further, most applicants in other countries have only lived in one country whereas most applicants to Buffalo have lived in multiple countries and hence greater checks needed. Having said that, a lot of people haven't even moved onto the processing stage.
I am guess it has to do with quota and CEC applications at Buffalo. For some countries, it could be security checks and for others still, manpower at the processing centers.
I am guessing all this. I have no evidence for any of the above.