That is true but we, the consumer, doesn't care about the cost. And with our pockets, we can dictate the price. The reason 70" + is still too high is because there are no competitions out there for Sharp. Samsung and Sony big screen TV prices are way too high. But with Vizio starting to come out with the 70" TV, I could see Sharp has to lower their price in the near future.
Its a niche market, only a select few are looking for 70" sets. If sharp wasnt moving their product at the current prices ,they would have already adjusted their prices accordingly. They are most likely content selling lower volumes at a higher margin and don't stand to gain much by significantly lowering their prices, all that will do is canabailize the sales of some of their smaller sets (which are less costly to make), which would result in a drop in over-all gross margin.