I haven't seen very many exclusive zombie maps (atleast not to either ZM or UGX), instead a lot of map are uploaded to ZM, UGX, GCZ, hex's site, pieman's site, and a bunch of other places.

Is there an advantage to uploading it to every custom zombies website on earth besides that it will never be gone forever? Because I sure as hell don't see one. (Besides trying to support those small startups!)

Exclusive releases are mainly just to either show loyalty from the mapper to a specific community or to show disapproval with another site's community. That's about it.

Well, that or laziness.

Is there an advantage to uploading it to every custom zombies website on earth besides that it will never be gone forever? Because I sure as hell don't see one. (Besides trying to support those small startups!)

More visibility.

I go with loyalty for uploading to one site.

There will be members on each site which are only members on that particular site. Uploading to each site ensures maximum downloads and views of a certain map. It's like if I am a distribution manager of a game, why would I just sell a game at gamestop when it would get to much more people selling it also at wallmart, target, and steam.

The only reason for exclusivity is what's stated above about loyalty. All the people that upload to other places likely don't care about issues on other sites and just want to get their map to people who don't necessarily know about another site or want to join.