On topic, RE6 is 20 dollars because for some reason, capcom vastly overestimated the popularity of RE and shipped way too many copies. They won't make the same mistake with Revelations.
Or another, correct way of explaining it: the game bombed and received too much fan backlash, so nobody is willing to pay full price or even half-price for it.
Initial shipments of 4.5 million copies were followed by another shipment of 300,000. Why ANYONE thought RE6 would meet or exceed the total lifetime sales of previous REs in it's first year is beyond me. But I'm glad you seem to think I'm incorrect, and RE is a franchise that should be doing that because of reasons. You've made a strong case that isn't full of fail.
Its cheap because the main hype is over and it isn't selling well anymore so they have to put the price down. I'm expecting it to be part of the essentials collection soon, then shortly after it will be £10.99 just like ORC is now.