4.0 ice cream sandwich - Could not see "persist.service.adb.enable" value from default.prop of Android device?

I read some guide to get the persist.service.adb.enable value, and it said that it belongs to default.prop file on device. Its content should be:

#

# ADDITIONAL_DEFAULT_PROPERTIES
#
ro.secure=1
ro.debuggable=0
persist.service.adb.enable=0

But when i connect device to PC (Linux), try to pull out this file from device (both emulator and Samsung Galaxy Nexus), the content of default.prop file is only:

#
# ADDITIONAL_DEFAULT_PROPERTIES
#

ro.secure=1
ro.debuggable=0
persist.sys.usb.config=mass_storage

So I could not see persist.service.adb.enable. Could anyone tell me why, and how can i got it?