"Microsoft is charging between 20 to 30%" - I think that's too much, it must be much less than that, but I don't know for sure.
http://www.wired.com/gadgetlab/2011/12/windows-8-store-intro...
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.