TBH I think Derek really needs the time to get into the flow of talking about his stuff.
I was going to say something similar.. it's probably Derek saying "um," and pausing a lot that adds length to the interview. Despite not being the most articulate dude, it's refreshing, because his answers are well thought out and honest, and he just comes across as a guy who loves games and making games. He isn't in sales-pitch mode, trying to generate hype or spewing a feature list; he isn't babbling pseudointellectual bullshit or claiming that gaming (or his game) is high art, and he isn't putting other products or people in the industry down in order to create drama and draw attention to himself.
Thank goodness that Derek has given us evidence that there are still people in the world that don't turn into a self-absorbed douche when a camera is pointed at them.