Actually, all images can be accessed with relative url's. The images that come with the wp install are accessed with relative url's - to wp-includes/images and to wp-admin/images. Even tinymce, wp-includes/js/tinymce/plugins/wpeditimage/css/, accesses admin images with a relative "url(../../../../../../wp-admin/images/...)".
One of the wp forum moderators has said "I've seen some discussion about storing images in a relative fashion but don't know how far that has progressed."
Personally, on my wp site, I removed the root portion of all the absolute addresses in both tables (a global search and replace in my editor) and everything, all my images and links, now work fine (and I have hundreds).
There is a plug-in "search-and-replace" which can be helpful to those sites where they build, edit, and/or maintain their site from behind a firewall or from a 'development" installation, perhaps a desktop installation (Javier?). That is not a solution, but it might help to fix all the links and images that are not working right now - if you have no other way of removing the erroneous paths. Using absolute addresses within a website is "generally frowned upon" for good reason. It assumes the site will never move, the website name will never change and, there is never a backup or development site. None of those assumptions are valid. Something does need to be done.