Technically (and legally), you don't own those apps. You bought the ipod and the apps that come with the operating system, not the apps that were added to it by the previous owner. They purchased those separately from the ipod and maintain ownership. If they have or will purchase another ipod touch or iphone, they have the right to sync those apps from their computer(s) onto the new device. Wouldn't make sense for Apple to give you that same right -- it'd be giving two people the products that only one of them bought.