Contrary to what you might think, the newly announced 2DS actually features a single screen, not two individual displays.
According to USGamer, Nintendo opted to go with a single touch screen and split the display into two with plastic casing. Since the entire screen is touch, the top half is covered by a protective plastic sheet.
This is clearly a move by Nintendo to cut down on manufacturing costs, as creating a single screen is obviously cheaper than building two into each device. Again, this only serves to reinforce the fact that the 2DS is clearly designed to appeal to a younger market and recoup the losses Nintendo is facing with each sale of the Wii U.