@elmer: I'm pretty sure that the 710 doesn't have a FFC either. As for large size display, I have an HD7, and I can attest that with a phone that large, it's an absolute PITA to swipe/touch the screen along the edge nearest your thumb when holding the device with one hand. With a smaller device, you can anchor the phone in the middle of your palm with your fingers wrapped around the far edge, which gives your thumb freedom to go (nearly) anywhere on the display with the device is still firmly gripped. Unless you have banana hands like Tony Robbins, it's kind of tough to hold a device like the HD7 (and most likely the Lumina 900) this way.
FWIW, Nokia was smart and placed the power button on the side (as Samsung does), which makes unlocking the device much easier on larger devices.