Fewer rows = fewer pax = less weight = longer range because the fuel you use can go further. This is similiar to what Singapore did with their non-stops to SIN. Since they wouldn't have been able to fly if all their seats in the original configurations were filled, they pulled some out & gave extra legroom- that gives them less weight in order to make the flights non-stop without re-fueling, but also is a nice benefit for the pax.