Of course it happens. Bad things and unexpected things happen. It is better to be prepared for them than not, etc. But saying completely predictable and trite things whenever some unusual bad thing happens is not 'a good argument'. It's barely even an argument.
The argument of self-hosting vs SaaS is still a valid one regardless of how predictable you might consider it. However the argument of arguing about arguments is definitely trite. But perhaps this is a good place to end things before it gets too meta ;)
Granted there are more cases of when SaaS et al works than when it does not. And I do agree with you that it's no ok to shaft paid customers in this way. But that doesn't mean that it doesn't still happen. This is why I've have to consider the self-hosted verses XaaS debate myself writing Business Continuity / Disaster Recovery / et al plans.