I think the Businessweek poll shows average incoming salary and average outgoing salary. It's an interesting way to look at how much each MBA adds to the bottom line, but I think the value is limited.
Schools that send a lot of people into high paying industries (banking and consulting) will do better; schools that send a lot of people to high paying locales like NY and SF will do better. The numbers will also vary based on percentage of career switchers at a given school, average prior work experience, percentage with advanced degrees, and a whole bunch of other factors. The most relevant thing to look at, I think, is the list of firms that recruit on campus. If they firms you are interested in recruit on campus, then you can make a case for landing the job; if firms you are interested in do not recruit on campus, you will be left with scraps only if they can't fill their hiring needs at their core schools. This is much more relevant than average salary or anything like that.