The Panopticon/Disappearing Talk Comments

Just a question and this seems like it might be the right place.

I'm noticing some pages that, in the little Talk navigation tab, indicate there are comments on the Talk page but when I click on it, the page is blank. Sometimes the number is small but sometimes it is not. I can see where a user would choose to delete an individual comment but these are just completely blank pages.

Is there a reason why Talk pages would be wiped clean and not have comments be archived? I would hate to think that any user would just come in and delete an entire page of comments.