In all seriousness, I would guess it's strictly based on what Specialized thinks they can get based on supply and demand. They may have a lot more Tarmacs than they have Roubaixs and therefore need to discount them more.

The future shock may also have something to do with it as it is something that is not found in a normal frame but I think it's just more likely that they have priced them with the goal of moving them all in a certain time frame.