Other teams infact have adopted it. Not to such extreme lengths as Red Bull, but both Ferrari and McLaren use shorter gears too then a few years ago.
It's of course not something that is without disadvantages. It leaves you more vulnerable during the race. A good example of that would be Monza: in 2011 Red Bull used unusual short gears for that circuit, but in 2012, when they did not had a performance advantage, they didn't opt for that anymore.
The gearing is set like that to match an aero philosphy. They haven't just gone "you know what, we'll run short gears, no one else will figure out what we're doing and adopt it" – the reason other teams aren't adopting it is because it doesn't match their slipperier car philosophy.
But that also works the other way around: shedding drag is useless without changing the gearing. It an and-and story.
Anyway, this all deviated too much from the main point: the car isn't more draggy by design. It is one of the best L/D ratio cars out there, if not the best.