Setting the pref from the product UI (Edit > Preferences > Commenting) sets:
[HKEY_CURRENT_USER\Software\Adobe\Adobe Acrobat\10.0\Originals]
"bPrintAnnots"=dword:00000000
Setting from the print screen sets:
HKU\S-1-5-21-762979615-2031575299-929701000-51250\Software\Adobe\Adobe Acrobat\10.0\Originals\bPrintAnnots: 0x00000000
hth,
Ben