For better or worse, when I was interviewing developers I would give specifically vague requirements, since requirement gathering is a skill that I think (senior) developers must have. I don't think that's a useful thing to do in a take-home assignment, though, since you can't clarify requirements with your client in that situation. That said, I admit that I would also expect error handling to be addressed in any piece of software written for any purpose.

Interviewing is a nightmare on both sides of the fence, though. There's a reason why it's a good idea to build up and leverage your network of coworkers.