How come 東/东 has a second meaning 'owner/master' or 'host'? Examples include 房东 or 财东 and 东道, respectively. What is the etymology behind this additional meaning?
東: 主人。由於古時主位在東，客位在西，所以稱主人為「
　　東」。如：「房東」、「店東」。

Translation: In ancient times, the host was seated to the east and the guest to the west, so the host was called "East".

reference:
http://dict.variants.moe.edu.tw/yitia/fra/fra01875.htm

Personally I have also heard it is because the Sun rises from the east, thus east is seen as the 'emic', or the 'theme'