For them it's 0.00...1% of their business. For a small customer who deployed on their service it might be 30% or more of their development budget. Of course that's the way corporations do business. But that's why as a small one you can't really trust any of them. You can just place bets and sometimes you lose.

To put it another way, it is an implicit cost of using AWS: You have to have contingency plans to cope with discontinued services, and you need to be able to realistically execute those plans. I think it is just another reason that AWS isn't as good a deal as it might initially appear to be for small businesses. (Larger organizations may have a better chance of amortizing these costs over many projects.)