A 100% true test is when you have the same hardware. Running windows on MBA is defect because Apple writes iOS for their hardware. So if we have a magical power to run iOS on another hardware and run Windows on that same hardware, then the test is fair. But that doesn't need to as windows-based tablets hardware are not always as polish as apple's.
They have numbers for your 100% true test. That is where the final 50% difference comes from.
2013 MacBook Air 13"
Under OS X: 14hr 26 min
Under Win8: 7 hrs 40 min
Though I am not sure I would call that 100% fair. Apple wrote the firmware and drivers used by each OS, so it has a vested interest in getting something out there that works but not optimizing for the competition.
Yeah, but what are you going to see in the real world? You are going to see OS X on Apple hardware and Windows on whatever random box the person had handy. Sounds pretty much like what they tested.
The test indicates something more important than Window's performance and that is monothilic designer like Apple can in fact make a great product if the designer chooses to. If Windows were to make their own laptop and invest the same amount of resource into bothe software and hardware, the comparison will be more interesting.
In essence, your average OEM does not do a great job. The capacitor, the transistors they use are probably way cheaper than what Apple have put into their MBA. That is expected because after all, your Dell computer is not going to cost $1499.
