To lure in would-be developers, Microsoft is establishing an attractive revenue-split model that trumps what Apple delivers to its App Store and Mac App Store software partners. The Microsoft split starts at 70-30, between developers and Microsoft, respectively. This is the same ratio Apple offers, but once an app has proven its success by garnering $25,000 in sales, the split shifts further in the developer’s favor to 80-20.
Also I am 90% sure that this only applies to metro apps, non metro apps will be featured in the store but users will be directed to a website (chosen by the application developer) to purchase/download the product from.
Store fees are calculated on a per-transaction basis as well. These fees are based at 30% of the app price, until your app reaches $25,000 or equivalent of lifetime sales (aggregated across app sales and in-app purchases) when they change to 20% of the app price.
http://www.wired.com/gadgetlab/2011/12/windows-8-store-intro...