Sources for TUAW say that they may have found possible hints of two iPad 3 and iPhone 5 models within the iOS 5 framework. Found in the USB device files in an unreleased iOS 5, the information found gives credible evidence to the above statement. However, no hints on a possible iPod Touch 5 have been found.
There are declarations in the system files found that reference an "iPad 3,1" and an "iPad 3,2." The same for the iPhone 5 - "4,1" and "4,2" (iPhone 5 is a fourth generation device). As mentioned above, there are no hints of the iPod Touch 5 found in the system files. Based upon this speculation, it may be true that Apple is reserving their September release for the iPhone 5, not the iPod Touch 5.
The article from TUAW made an important note:
Of course, experience has shown that model registrations do not mean that these items always become an actual shipping product. For example, it took almost a year for the iPhone 3,3 (the iPhone 4 for Verizon) to ship, and the iPhone 3,2 never became a product. Sources believe that's because alleged carrier deals probably fell through for a third iPhone 4.