And what happens when you spill your coffee on paper maps? No system is perfect.

(not that an iPad is immune to the cup of joe either)

It's harder to make a paper map useless than to make an iPad useless.

Of course a protective case and a spare would solve that problem since I assume flight crews are used to operating in an environment where they are surrounded by sensitive electronics that they really don't want to break.

never mind that, what happens when you're cruising along at 30000 feet and apple decides your app is no longer approved?

  This is the captain speaking. Does anyone onboard have an iPad we can borrow?

/humour (just in case someone feels the need to explain the problems with that idea.)