First of all I would like to apologize for misleading you - this text should have been removed from the documentation as it was valid for the first version of RadEditor for MOSS. Thank you very much for pointing that out for us - we will update our online documentation as soon as possible.
RadEditor for MOSS can be used in all scenarios under IE. Please check the Installation and deployment / Using RadEditor in List Items
and this screenshot
for more details.
Your points were updated for bringing this problem to our attention.
the Telerik team