I don't know what the problem might be. I tried to do the same here - created a personal site, made sure that the features are activated from site collection features, then created a blog site, and finally click on add new post. The RadEditor was on the add post page and worked OK.
Open the \Program Files\Common Files\Microsoft Shared\web server extensions\12\TEMPLATE\CONTROLTEMPLATES\
folder on your server and check if the RadEditorList.ascx
is present there. If yes, then try restarting the MOSS web application and/or the MOSS web application pool.
the Telerik team