It seems that this problem of relative links being useless carries over to the use of templates as well. If you have a template and that template has place holder images in it then the following problem occurs. When you go to insert the template and view the thumbnail of it, if you have relative links set appropriately in the template they show very nicely in the thumbnail. However, when you insert the thumbnail into the WYSIWYG the relative links for the place holder images are no longer correct and the images show as being missing. If you adjust the template so that they work inside of the WYSIWYG then they don't show properly in the thumbnail. The only way to make them work both places is to use absolute or site relevant paths for both the editor settings and in the template itself.
When you get right down to it the only place that you can use relative links is if you modify the HTML directly. The WYSIWYG does not modify them as it did in older versions. Other than that relative links just don't seem to be useable.
If you know a way around this that allows the use of relative links inside of templates or for images (and I assume also for documents or anything else that you insert) please let me know.
If this is on a list of future enhancements I would also appreciate knowing that.