Thanks for that information, Carlos. I should have mentioned that this script will be running on Mac OS X, 10.9 and eventually 10.10.
Just to be clear, it works fine here as well, IF the PDF Presets window (Edit > Adobe PDF Presets...) has been opened and closed at least once after the application was launched, just as originally reported by Ben. It actually doesn't matter if one presses "Cancel" or "OK" to dismiss the window; just that it be opened and closed...
Also as reported, in the ESTK, the property simply does not appear in the Data Browser. In Script Debugger's data explorer (AppleScript), the error "an Illustrator error occurred: 1128353350 ('FNAC')" is shown.