In a way, there is an element of self-selection. During med school A LOT of people want to return to where they are from - be it east coast or west coast - because the stress of med school makes the adjustment to the "opposite coast" just a tad harder than usual. Personally, I think there is a degree of the coast orientation during your college formative years that makes you want to go back too. Also, compared to the rigid structure of medical school, any professor/colleague you had in college would seem much more liberal and pleasant that people consider it to be a coastal difference rather than a microcosm difference.
Although, I think PDs and faculty have some bias too. Chances are, they have seen a broader spectrum of students from the same coast due to the ease and low cost of doing away rotations at schools nearby. Within this broad specturm, you are more likely to find good students than the relatively fewer number of students visiting from the opposite coast. This is how the reputation of a school comes about - direct perception. There is just a larger "n" from the same coast than the opposite coast, and they can always come up with student X from the same coast that is better than student Y from the other coast.
I'm doing good 🙂 How're you doing? (getting ready to move to SF yet? I was just there two weeks ago for a conference and I absolutely want to move back)
