This model is pretty unfamiliar to me. At the company I work for, we are being paid by businesses to deliver the full service for an application that they are requiring: planning, specification writing, coding, testing, deploying, maintaining. But, even though we write the code, the payer has full rights over the project (even the code). They can, anytime, dump us and find another 3rd party to maintain/modify that software
A company from Taiwan (or Korea, Japan, the US, etc.) has created an MMO that it now wants to run all around the world. While it may be able to run servers in their home country/region, often times it does not have the expertise, credentials, or resources to run, advertise, monetise or maintain the game overseas.
Hence Game Publishers like GameForge come in who will pay you a certain amount of money per year to be granted permission to run your game in Europe. GameForge has server infrastructure in Europe that can run the game servers, staff that speak the language of the community (mostly), it has established marketing channels, a wide array of payment methods and has the experience of running a game in a market with different culture, customs, and laws.
You will even see that on the Steam shop pages for all kinds of games, e.g.:

A small game developer studio may be able to create a game but lacks the manpower and know-how of selling and marketing it worldwide. So, they find a publisher who, for a cut of the money earned, will take over all that.
As such, GameForge really is just an intermediary that takes care of the game servers and communities, while development (sometimes) happens @ RuneWaker in Taiwan.