I don't want to state the obvious, but different laptops have different capacity batteries. Atwood was comparing the 11" MBA to the Surface Pro 2 as they have similar battery capacities (SP2: 42 Wh, MBA: 38 Wh), and - as Maakuth notes -- are both made by companies in control of both software and hardware. The fact that you can find laptops with higher capacity batteries that have longer battery life doesn't prove very much.
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.
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.
First Samsung laptop review I read, a NP900X3E-K01US with a 44 Wh battery:
...battery life is disappointing for such an expensive laptop... [1]
Second, a Dell XPS 12 review:
50WHr battery ... Wi-Fi browsing test ... seven hours and 58 minutes
[1] http://www.cnet.com/laptops/samsung-ativ-book-9/4505-3121_7-...
[2] http://arstechnica.com/gadgets/2013/10/review-xps-12s-haswel...
* There is not a battery life problem on Windows machines.
* The battery life problem on Windows machines is not surprising.