Reflected light is softer, and more diffused. Backlighting basically directs the photons straight out of the screen - it's like looking into a flashlight, vs looking at a flashlight's light on a wall. Backlit displays ARE harder on the eyes
That makes absolutely no sense. That's just pure junk science.
The light coming from a emissive screen is actually quite diffuse. You know how in the movies whenever you see somebody sitting in front of a screen in a dark room you can see whatever's on the screen projected on the actor's face as if from a projector? That doesn't happen in real life, because light coming from an emissive screen (like a laptop or an iPad) is very diffuse. That it, it's shining out at all angles with a high degree of divergence.
There are really only two things that affect how your eyes feel: total illumination, and distance. When there's a lot of light coming into your eyes, this causes the irises to contract, which some experts thing contributes to eye fatigue but nobody knows for sure. The bigger factor by far is the muscular effort of converting and focusing your eyes, which anybody who's ever worked on a 3D film knows is enormous. Improperly converged stereoscopic projection can actually be physically painful, because it forces your eyes into a configuration they're not used to. It's analogous to holding a book at arm's length. You can do it for a few minutes, maybe longer, but eventually your arm's going to get tired.
Computer screens are typically (not always) farther away than most reading material, which makes your eyes converge to an unusual distance. This contributes to eye fatigue. Computer screens are also typically much, much brighter than they need to be, which doesn't help.
The iPad is handheld, which means you'll hold it like a book most likely, which helps with the convergence issue. And if it's built like the iPhone, it will attempt to match its brightness to the ambient light level.