I believe a slight roll off of the throttle would result in a slight weight transfer forward, which is effectively the same thing you are achieving with the hook turn technique, shifting weight forward, compressing the fork's which results in a shorter wheelbase, netting you a tighter turning radius or line.
now completely chopping the throttle will probably not get you the same results
Eventually. But that is after some other undesirable things might happen, including running wide. As someone else pointed out it violates Rule #1 of throttle control and isn't in the list of exceptions. Check out Twist II the DVD - it gives the science behind why you'll initially run wide if you close the throttle mid-turn, and also why eventually your line will tighten. Despite the shortening of the wheelbase there is initially a change in the contact patch of the front tyre and an unintentionally induced countersteer the wrong way. Eventually the bike slows down etc. and your line will tighten.
But the DVD explains it a lot better than my few sentences do!