I did a little test with sitemap. Created a web site with different internal links but added other pages in the sitemap, which are not linked from anywhere. I wanted to see if Google would index those "invisible" pages following the instructions in the sitemap. After 2 months, all the linked pages are indexed, but none of the pages only present in the sitemap. I guess backlinks and normal indexation is still much stronger than any good sitemap. You experience the same results?