As all app marketplaces Microsoft’s cut for every sale is 30%. But non-us residents had to also pay taxes in the U.S. in addition to the taxes in their own country. So their payout would be far less than 70%.
One way to get around this was to apply for a U.S. IRS individual taxpayer identification number (ITIN, W7-Form) and then send a certificate of foreign status of beneficial owner for United States tax withholding (W8-Form) to Microsoft. The whole process used to be a pain in the back but as of August that has changed. Microsoft only asks for the W8-Form without the ITIN.
So for everyone living outside the U.S. who has not applied for an ITIN yet must now only fill out the W8-Form which can be found here and send it to Microsoft:
Microsoft – Windows Phone Marketplace
Attn: Finance Department
29011 Commerce Center Drive
Valencia, CA 91355
The whole FAQ regarding the Microsoft Marketplace can be found here.