distinguishing between nodes and comments

i don't understand why drupal separates comments out as a distinct
content type. it seems like it would be better to consider everything as
a node, ie. inherited from a node type. this would potentially enable
a common display framework with different renders. it also seems like
having all node type be identically defined, that is no second class
types, would help make the content rendering easier. eg. the node table
types would be anything defined by the taxonomy and the base set could
be the standard story, blog, page, etc. types. the legit content would
the simply be defined by the type tag. additional tables could be used
to house the sub-classed type's attributes.