thank for your reply @tbobker. Site Variables are indeed a very powerful feature, and your link is ineed very helpful. For this specific problem though, those techniques doesn't seem to go around the fact that zones still need to be manually linked with the campaingns (directly or indirectly through the banners), and this generates huge amounts of maintenance for our usecase where there'll be several of Websites/Publishers vs thousands of campaings.
I get what you say about having a single zone, and that is very tempting, but wouldn't that also imply having only 1 Website/Publisher as owner of that zone? If zones could be shared accross Websites, would be great, but the zone lifecycle seems to be completely dependant from their parent Website. So, asuming we need several Websites (mainly for statistics), it follows we also need corresponding many zones.