There was an IgnoreTarget option in opera:config that allowed to open all links in the same tab regardless of target attribute (i.e. target="_blank"). I would implement this one globally, but included ability to override it in Website Preferences.
It is annoing on some sites that you need to close each tab with opened link instead just going back. Example of such web site: http://vott.ru
@fatal, I can consider that, for now you can use OpenLinkInCurrentTab in custom webWidget menu.