Actually I've weighed a stock rocker and a comparable 1.84 Yella Terra roller.
A stock rocker weighs in at 80.5 grams, vs. The roller at 69.9. That's a close to 130~ grams of weigh savings across the valvetrain alone, without even counting the pediatals and rockers. Lighter valvetrain parts also do their fair share of lessening the load on the hard parts, due to less friction and wear on the guides.
Not sure where you got your info there, but you must have used some of that Detroit engineering math to solve that equation.