Well here's the dillio as far as I understand it:
Partner API - resells FT photos directly = the same price.
Business API - "(c) ...You shall charge an amount for the End Product that exceeds the aggregate Fotolia Price for each Work contained therein." (everyone gets paid) The Business API is for derivative works = tshirts, mouse pad, etc.
Developer API - must be non-commercial (plugins, aps, etc)
The ONLY interesting part of this is the Reseller API and to be honest, they don't have ANYTHING about it in the Terms of Use - I'm not even sure it's ready to go yet. Until we know that, we won't know what's allowed & not allowed or how FT & its members get paid.
(On the Documentation Page, there's no line for Reseller API)
Get an Api Key <--- This link isn't active/valid yet.