i really would like to see these studies. because everything ive looked at shows vaporizers to be comparable and rarely better, let alone double. you dont lose as much due to breezy smoke and what not, but the actual thc you can get out of the same amount of bud is the same or slightly less than when combusted. so maybe your figures are based on the amount of "released" thc...in which case you would get almost all of it, because it doesn't drift away.
see here
however, it's worth it just for the reduction in cannabanoids and other toxins (and the efficiency with not losing smoke) in my opinion.