Why does AR use base_class for polymorphic relationship "type"

I have a couple models that inherit from a base class that then
inherits from AR.

When they are used in a polymorphic relationship the "type" is always
the base class.

Just curious if anyone has a reason why it doesn't use the *actual*
class rather then the base_class. I have patched AR to use the actual
class if !base_class.table_exists? but it adds another query each time
(which in turn fails some of the rails tests).

My only guess was for use with STI, but even then I am not sure if
there is a better solution then using the base_class

-Eric

By default, Rails stores the class name that corresponds to the
*table* name that the record is from (to avoid storing duplicate data
for STI subclasses). If you're actually storing the subclasses in
different tables, you'll probably want to do 'self.abstract_class =
true' in the base class to make this clearer.

--Matt Jones