Hey Andrew - Art Sumo works by sending out weekly emails of original art from around the world. You can purchase the painting contained in the email if you get to it first.
About the question of why this format, we decided to go with this to 1 - let people passively stay connected with art from different cultures and 2 - to create a sense of excitement to see each painting 3 - it replicates a gallery experience more closely where you examine paintings in this manner and 4 - when the paintings are directly marketed like this, the paintings sell.
Sure others are selling socks and diapers in this manner (via regular updates groupon style) as well. You can also buy those products using different channels as well (like art).