Found out today that the behaviour of the PublishingWebControls:EditModePanel changed between MOSS2007 and SP2010.

Apparently,now in SP2010, you need the EditItem Permission to be able to see what is in an EditModePanel even if the PageDisplayMode attribute is set to "Display".

So basically it works like a SPSecurityTrimmedControl

Example:

<SharePoint:SPSecurityTrimmedControl PermissionsString="EditListItems" runat="server"> 
</SharePoint:SPSecurityTrimmedControl>

Update
This behaviour has been changed back to 2007 behaviour as of SP1 for Sharepoint 2010