When you switch countries, you will see your Purchases list depopulate, because you haven't made any purchases from the new store. You also won't be alerted to updates for purchases from the old store. However, if you should hear of an available update for one of your apps and that app is sold in the US store, you will be able to get the update. At first it will appear that you will be charged for the new version, but in the final steps the new app store realizes that you previously bought the app and download the new update for free. Once you have updated an app through the new store it will appear in your purchases list just like the new apps that you buy in the new store and you will be alerted to future updates.