Do you remember which USB mode your GS3 connected to your computer with? Was it USB Mass Storage mode (sometimes called USB Disk Drive mode)? That mode allows your computer to see all of the phone's folders (except for the protected root system folders). More recently, phones and tablets only offer MTP (Media Transfer Protocol) as a USB connection mode, which allows the computer to see only some of the folders. This restriction has to do with the fact that most devices now have unified storage, which allows the entire storage memory to be used for app installation. Older devices that had USB Mass Storage mode as an option typically had multiple partitions, with only a relatively small partition available for app installation.