Not literally rotting ....LOL....
"Lot Rot" is dealer slang for units that nobody wants to buy, either because they don't have a good floorplan, the right features, etc. In other words those units will sit there and rot on the lot before somebody will buy them....if the dealer is paying carrying costs on those units he is more than likely willing to write a killer deal so he can free up cash to get the new 2015's on his lot.
I would go and look, see if you could see yourself camping in one and what kind of a deal you can get on it. If not, you'll have a clear picture of why he hasn't sold them yet...