USB keys are susceptible to damage, as well as loss.
And cloud storage isn't ?
Cloud storage is nothing but a bunch of servers in a datacentre, infact, its worse than that, because they generally use cutting edge unproven software architecture to spread the files around.
Everything is susceptible to data loss Mr Captonian, everything.... that's why I keep banging on that you should have a minimum of three independent copies of your data at any one time.