FAT file system provides an option to quickly scan for files/folders using the Quick Scan option. If the option lists the desired files/folders then you can recover them.
Deep Scan option gives better results (and is used when Quick Scan lists less or no files) but takes more time.
In case of HFS, only one option of scanning for files/folders is applicable.
This is why you get two scanning options on a FAT based hard disk but on a HFS based hard disk you get only one.