Throughout Europe it is fairly typical that businesses are closed on Sunday. Even if a city isn't very religious, seems that the longstanding convention among shop owners is that Sunday is a day of rest. For the regular person or tourist, this also means don't figure on being able to purchase anything on Sundays.
In the case of the city of Amsterdam, it has long been possible to buy things in shops deemed related to tourism. Though, as many owners have complained, it becomes difficult to point to many types of shops as not tourism related somehow. Perhaps thanks to these complaints or the general feeling that people really want to be able to shop on Sundays, the deputy mayor of Amsterdam seems to be going forward with a plan to allow any shop that so wishes to be opened on Sunday. If the city council agrees, you will soon see a lot more activity on Sundays in Amsterdam.
