I think Derrick Bolton (if you don't know who he is - jeez! what kinda rock have you been living under?

jus kiddin' - He's the Director of Admissions, Stanford GSB) made most sense when he said not to obsess over the percentages and probabilities of admits if you receive an interview call. Since the result is pretty discrete - an Admit or a Ding - so analyzing figures and numbers would present a wrong picture.
I'd evaluate the interviews on the following lines: Since most top tier school admit ONLY after interviewing, the interview means that they're interested. It's like that first blind date you go out on after hearing about that girl (or guy) from your friends ("She's really smart!" or "He's really funny!"). But during the "date" , if you are not exactly what the words on the application projected you as, then that second date is pretty hard to come by.
I guess if one receives an interview call, then one thing's for sure: the application was interesting. So kudos - you've got good writing skills (and also probably means that you've got friends who have good editing skills!). All of that is good news. So let's chill.
Now, again, what was the interview to acceptance rate of HBS?