In a debate, when it is based on answering moderators questions, the person who speaks first has the advantage of setting the direction. The person who speaks last has the advantage of saying things that do not get immediately refuted.
On the first question, Obama spoke first and Lehrer was going to proceed to a new question after Obama had spoken a third time and Romney only twice. Romney stopped him and said, "He spoke first, so I get to speak last." The contest was over at that point, Romney had won. He had removed Lehrer's ability to provide an advantage to Obama, he had shown command and control in a presidential manner, and he flatly pissed Obama off. Neither Lehrer or Obama recovered after that.
You are wrong about the distribution of time. When I made a point about this first exchange, my wife started score keeping. Obama ended up having the first and last word at a 2 to 1 margin over Romney. Unfortunately for Obama it was because he was performing so poorly that Romney didn't need to respond.
Even the time when Obama said, "I still had 5 seconds left when you interupted" and then spoke for another 30 seconds, Romney didn't have to make a point of it because that 30 second ramble did more harm to Obama than to Romney.
Great summary & recap of Romney owning the debate!