Viki's model is crowd-sourcing their subtitles, which entails an army of volunteers who are usually passionate about what they do. When a new episode comes out English is usually the first to get done, which often acts as a template for the other languages. Even here, though, there are signs of change: some of the newer titles Viki has are sublicensed from Kocowa, the consortium created by the three main broadcast networks (KBS, MBC, SBS), and thus the English subtitles on those are done professionally by Kocowa. They're also made available first only to those with a Viki Pass Plus subscription, then to those with Viki Pass and finally to the ad-supported free viewers.
A more in depth look into the Viki community of subtitlers and the K-drama community in general has just been put out by AP: