Samsung uses a shadow mask that has holes for the pixels where they want to lay down the OLED materials. The mask is extremely thin and for a 4K display needs to have 8 million tiny holes for each individual pixel. As the screen size gets bigger, these masks lose rigidity and yields go down. Samsung tried to produce a 55" OLED TV but they never managed to bring the costs of the display down.
LG simply coats the entire display with each OLED material. They do have to add a color filter which adds to the costs but that is offset by much higher yields for televisions.
Samsung's process works fine for small displays and LG will use the same RGB architecture for mobile but televisions are another story entirely. I'm not sure which will win for monitors though.