I struggled quitea bit to be able to set up my moderator account. Until I allowed all posts and pages capabilities and now the can finally moderate comments. I didn't deactivate one by one precisely to see which would remove this. Nevertheless I couldn't find any documentation anywhere about this. Onyl when I found another plugin review...
Ordinarily Wordpress only allows Editors and Administrators to moderate comments, and both roles require those capabilities.
This page from the Codex does an excellent job of explaining roles and capabilities:
You can manually create a new Role and assign to it only the capabilities you want the Role to have, so that those you designate to moderate comments can, or not, have the ability to create/edit/publish posts.
Alternatively there are several great plugins that allow you to customize capabilities based on Role, as well as add new Roles, etc. I would encourage you to try one in order to tighten up who can do what.
One that I've used and really like is this one: