Here are two comments get deleted because of "being answers" in Why aren't superbugs weaker than their wild type?
First, I want to say that I don't have any objection on deleting answers in comment. It's inconvenient, but it's necessary. However, I don't think that these two comments are answers.
The first one is classified as implying an answer. Carey is surprise because he is reading something unbelievable ("I don't understand your reasoning..."), and asking for clarification. Asking for clarification can be in calm tone ("Why do you think this?") or in surprise tone ("What? Why do you think this?"). The latter can imply an answer, but first and foremost it is a way to showing expression, and I don't think it is an answer. Even I, the asker, cannot think it is an answer.
The second one answers on my previous comment ("why do I get downvoted?"). As YviDe saying below, it is to answer a comment, a thing that doesn't relate to the question. Yes, it is an answer, but it's an off-topic answer. Even if it will be used later to the on-topic final answer, in this form it is still a comment more than an answer, and shouldn't be deleted.
Talking about off-topic answers, what if they are there to answer an example? Say I give an example to back up my thinking, but unfortunately use it wrong. Would someone answers on that example only violate the policy? After all, it's just a minor answer which doesn't answer my major question, which is lying on the title. Writing it in the answer section seems to be off-topic.
One more thought. We can see that some users are not happy with this site. I think it is because of this policy: their contributions get deleted. We should be clear on what is an answer and what is a comment.
What do you think?