"the ones in the leather sleeves would tend to have a better chance of surviving the experience."
Definitely; the cases will certainly be in better shape, and compressing the leather on impact is going to reduce the G forces. (A neoprene sleeve would likely do even better on the G, like an airbag, but not survive the friction.)
Rather than hazard a mega$ Mac in experiments to test this, a cellphone duct-taped to a piece of steel the same size as the computer would probably be the subject of choice. It could transmit the accelerometer readings throughout the "flight".
I'm assuming the metal case of the tablet would slide reasonably well also
Horizontal braking would have been quite gentle, as long as there was nothing in its way to hit.
That's as may be, but my gut feel is that if you repeated this experiment with 100 computers au natural and another 100 in leather sleeves, the ones in the leather sleeves would tend to have a better chance of surviving the experience.
The forces involved in that incident are interesting to consider.
Although the Mac obviously fell a couple of metres, it probably wasn't the equivalent of a flat drop. At freeway speeds, even a small plate is going to generate quite a lot of lift, which would slow the descent. If it hit the vehicle on the way down, that would have absorbed some of the potential energy.
If turbulent flow had it hitting the ground on edge, damage would likely have been much worse.
Horizontal braking would have been quite gentle, as long as there was nothing in its way to hit. Leather slides on concrete. (That's one reason motorcyclists wear it.)
... leather looks better with age (I, myself, am maturing like a fine cheese)
Regarding the sleeve shown above, I know that it would look awesome "in the flesh" as it were -- all it needs is a bit of Chamberlain Leather Milk Liniment to give it a new lease on life -- the scuffs and scrapes just give it character.
Meanwhile, I've been carrying my Saddleback Messenger Bag everywhere with me for more than a year now -- including back and forth between home and my office every day, and also on every business or vacation trip I take -- and it doesn't have a mark on it (curses). It's going to take me 20 years to give it that lived-in character, by which time my son will be pestering me to let him have it (like that's ever going to happen LOL)