op: I'm not aware of any transfers being accepted from other schools. However, Northwestern does take transfers into the program from its own undergrads.
kreno: It depends on the program and who you ask. I believe what you said does apply to the program here at NU. The school tries to find students who know they're pursuing medicine early on and who seem to be capable of handling the work. Once we're in, there's a lot of freedom, and fairly minimal standards to keep up, but everyone still works hard. And I really think people get to pursue their interests and do. Based on comments from the faculty, students coming in through BA/MD perform as well as the regular admissions students.
At the same time, some people who apply for this kind of program don't share the philosophy of taking away the pressure. They get in and NU essentially becomes their safety school and they apply out to other places. I don't think there's anything wrong with that either. Every year, some people leave and its usually to more prestigious schools like WashU, Duke, or UCSF. Personally, I'm happy for them and think it reflects well on the program.