I also use custom field inspectors for my tables. Another way to make them show up as not editable is to use two different ItemRenderers for the field inspector. I create custom field inspector ItemRenderers, some are editable and some are not. When I have the editor turned off I can set the editor for the field inspector to the non-editable ItemRenderer.Below are two different ItemRenderers for the field inspector editors that I use. When the editor is active I can set a field inspector to use the rFST1 and when not editing I can set it to rFST2.
protected var rFST1:ClassFactory = new ClassFactory(fiFieldRenderer_Spinner);
protected var rFST2:ClassFactory = new ClassFactory(FieldRenderer_String_No_Edit);