Consider it as two components, for the vertical component the difference is none compared to dropping it from a static car window. It's still going to fall a meter or so before hitting the floor. The only difference is in the horizontal, now assume that the nano was dropped onto a perfectly friction free surface, there would be no deceleration, no bumps, no scratching, no difference to it being dropped while stationary. As it wouldn't change horizontal speed and as such wouldn't suffer from any acceleration.
Now the difference is that the surface isn't smooth, and as the ipod moves along the floor it gets caught, spun, scratched and bumped by the tarmack. However it's not being stopped imediatly, the deceleration it's going through isn't going to be that great. @ 50mph it's traveling at aprox 22mps, if it took 10meters to come to a stop then it will experience an average deceleration of 2mps^2, or .2g. And since a car takes about 15m to stop at that speed it's a conservative estimate of the Gforces (or not as that's the average, and it'd probably get much greater G forces as corners or edges get caught by imperfections in the surface. but hard drives can take tens to hundreds of Gs when deactivated, i'd expect Nand memory to do the same)
If it was fired from a canon at a brick wall at 50mph then you'd see a massive difference, or if it fell from the car window and bounced into a wall you would as the decelleration would be massivly higher. But simply grinding along on the tarmack is effectivly taking a rough piece of sandpaper to it.