I believe the | symbol signifies that what follows is a registry value (String, DWORD, etc.).
It would work (and I'm pretty sure it used to) if the path was: HKCU\Software\Microsoft\Office\11.0\Common\Internet|UseRWHlinkNavigation
where "UseRWHlinkNavigation" was the string value.
But the path is actually: HKCU\Software\Microsoft\Office\11.0\Common\Internet\UseRWHlinkNavigation|UseRWHlinkNavigation
where the first "UseRWHlinkNavigation" is the subkey and the second is the string value (there is also a DWORD value named "UseOnlineContent" in the subkey).
I suspect that a recent Microsoft update created an additional layer in the registry structure. I use a winapp1.ini with customized cleaning of Office 2003 so it's not a problem. I only noticed it while checking something else but if there are other reports of Office not being cleaned, this is probably the reason.
EDIT: After further experimentation, more weirdness ... having deleted the "UseRWHlinkNavigation" subkey several times, the string values now form directly under the "Internet" key and the old command line with | instead of \ works. Despite being deleted just as many times, the "QuickFindMRU" and "StripSearchMRU" subkey levels are still being created and the old command line still will not work. Just a glitch in my software? ... or did Microsoft's patches on Tuesday change something again?