Comments are not nodes mostly because nodes are perceived as heavier. However, hook_comments are more or less equal to hook_nodeapi so this is just a matter of actually registering which nodeapi implementation operates on what call. The seed for this is the module hooks registry. Second, currently we load all comments for one page in one query. This will be a possibility for most cases once we have join/foreign key info in schema API. Both of these require a lot of discussion and work so do not hold your breath. But I wanted to blog this so when the comments-as-nodes discussion again and again starts, I can simply point here.