that is ONLY true for the "local" folder (ie the folder containing the itc files for the songs with embedded album art. worthless imo because if the song has embedded art you can simply get the artwork from the file) so you will still be unable to view the album art for songs where you used the itunes advanced->get album art function. there is no album persistent id in the itunes XML.
that part should actually not be that hard. what i am doing is parsing through the .itc byte by byte and extracting the data that is contained inside. one piece of data is the persistentId. this matches up to the persistentId that shows up in the itunes xml for a particular song/album.