Ok, I am trying to figure this out, so who will provide the feed on december 2016?... what happens if the person doesnt enter the result or enters a wrong feed?
Right now settlement is dependent upon the creator of the asset, so in that respect settlement is centralized. Eventually, price feeds similar to smartcoin price feeds will allow for a completely decentralized solution.
The price feed is the median of many sources that are updated at least once per hour.
https://bitshares.org/technology/price-stable-cryptocurrencies/If the asset is not settled correctly, then money will not be distributed correctly. The market resolves to a condition of true or false, so it is pretty hard to get wrong, unless the creator is malicious.