You shouldn't be so dogmatic. I use both primes & zooms of varying focal length for interviews. 100mm isn't that long, often I'm at 200mm or more other times I might be at 11mm. It really depends on the shot.
Not being dogmatic at all, just answering the original question and saying that I've found myself using the 24-105 the most for interviews because it's so flexible. If using more than one camera I'll often use primes but as you say, it depends in the shot and the logistics.