Nope, they are cut from the same mother glass as the 77" so I expect there is a lot less 48" models being made than the 55 & 65 so can keep the price higher and they have zero competition in this area too.You assume 'good demand' is us fellow gamers, buying lots of 48" gaming TVs.
Us gamers are just a drop in the ocean of people buying TVs.
I believe the cost of making these are still quite high and a 48" is most likely made from the same cut of glass the 55" are made from, so they are likely going to be of similar price for a long time.
http://www.businesskorea.co.kr/news/articleView.html?idxno=34962