my ancient pocket pc in the cheap case that came with it, survived a shoulder high drop onto and down a few steps (had it in my shirt pocket, then when running down the stairs, it slipped out and fell down the rest of the way. it still worked and had no scratches or dents.
an ipad is easier to break as they made the glass thinner and also because the glass is not supported in the center (which it cant be)
the iphone 4 breaks easily also because there is no buffer areas for impact.
if you were to take apart something like a hp ipaq rx3110, you will nothce that the outer frame forms a boarder of empty space, the device can be made much thinner in all directions but they did not. Have you ever wondered why so many older devices did this?
it is because when you drop a device, the unit flexes. the added space allows the outside to flex while the fragile internal components remain unharmed.
look for high speed footage of electronic devices being dropped, you will see odd things such as a device that feels sturdy looking like jello when it falls.
devices designed to handle this have a buffer zone inside in order to prevent the energy from the impact from being transferred to the internal components, devices like the iphone don't.