Windows 8 Battery Life

So I'm looking at laptops on the Sony site and I notice that it's possible to pre-order VAIOs with Windows 8. Sounds pretty cool, I guess. I click on the S line and look at the comparison chart. The S Premium gets "Up to 4 hours 30 minutes" and the regular S gets an even 5 hours. When I checked a couple weeks ago back when you could order models with Windows 7, the battery life was marked down as up to 6 or 7 hours.

What's the deal?