I don't know why,I just know that they don't work(some degree).
Think this one the things they might be working on for the new UI,this only a guess.
Also think the codes are not complete or written as they should be.
Example:
The toolbar panel.
The book 14 has the very first code:
<PanelFile ID="ID_UISkin_Toolbar">
That first line doesn't make the code work for some reason,so if you tried to modify it with the width etc,it won't show up ingame for some reason.
But if you replace that code with:
<PanelFile ID="toolbar">
Then everything you modify in that code will show up ingame.
Its wierd,by the way that code I got from looking up from varies Authors xml here.
To be sure we need Frosty to confirm this.