There are number of things in Dempsey's book that aren't explained as well as they could be; on the other hand there are some things that make a great deal of sense. In general, you don't want to shift the weight onto your front foot when you jab; sure you get more pop on it that way, but it plants you in one place (making you vulnerable to counters) and it makes your right hand follow -up a two part process. Because your have to rock your weight back, then forward, to throw a proper right hand.
The 'power' in that move, like the Cotto clip you posted demonstrates, comes from the right foot propelling your weight forward. This also encourages you to bring it along with you, which makes it easier to throw follow-up punches, or to move away afterwards.