I think the article is asking the wrong question. A better question is: why does Apple (OSX/iOS) have such awesome battery life? After all, it wasn't always this good, or rather, it's been improving by leaps and bounds, both with new hardware and with new OS versions.
I think the answer is that Apple really, really cares and has been extremely focused on power/performance for a number of years. It has the focus, the institutional awareness and know-how that's been built up since around Tiger, and last not least the people on their performance teams.
Exactly. Apple learned a lot working on resource-constrained mobile platforms, and they brought a lot of that knowledge into OSX (one of the benefits of not having separate divisions?).
Back in Lion, the Mac would began suspending/killing processes in the background:
Devs and ubergeeks got upset ("Steve Jobs is taking away control of our desktop too!"), but obviously we are seeing the benefits with battery life. And Mavericks goes much further:
Update: If there's any doubt how seriously Apple takes battery life, note that their WWDC 2013 talk/video on "Maximizing Battery Life on OS X" was given by Bud Tribble.
I think the answer is that Apple really, really cares and has been extremely focused on power/performance for a number of years. It has the focus, the institutional awareness and know-how that's been built up since around Tiger, and last not least the people on their performance teams.
That's how you get great battery life.