All domestic US carriers exclude coverage for valuables including, specifically computers. If your Nook is damaged, lost or stolen in checked luggage, you are SOL and most baggage insurance + homeowners + CC policies exclude anything excluded by the carriers.

You should never place valuables in checked luggage.

As to TSA, it does not "have to" open your bag for secondary, but may well do so because so few people check electronics that it is likely a matter of suspicion that you do so. As you have found, the net impact is that you have a card from TSA saying they did it.