Unlike WiiWare, royalties to developers are not held until a certain sales threshold is reached.
Games published for Nintendo's DSiWare and eShop services are not required to reach a sales threshold before royalties can be paid to the developer. This is in contrast to WiiWare, for which a minimum number of downloads must be reached before royalties are released.
We spoke to Nic Watt, creative director of Nnooo, recently about their download titles. He told us that since WiiWare games require server support and uniformity testing for all titles, regardless of how well they sell, this is partly a measure to recoup costs. Whilst a final specification for Nintendo 3DS was not available, the eShop is thought to have the same policy as for DSiWare and as of now we don't know of any sales limit for 3DS downloads.
Our full interview will be up shortly.