I have a hunch that only international students go through the interview. I don't know anything about the deadline for the admission emails, but I assume they're still debating who's in and out if they're only going to let me know by the end of this month.
Just got an email from a PI at MIT which I had not mentioned in my SOP, in order to schedule a phone call to "learn more about my interests". I assume this is their way of conducting interviews, and I was curious if anyone here had one.
I agree with what you said about the narrowing of interests in the SOP. To me the ability to choose a POI after you get accepted to the school is what made me apply to the US in the first place.