The PostgreSQL License requires "LICENSE" file?

Hi,

PostgreSQL is released under "the PostgreSQL License".
http://www.postgresql.org/about/licence/

I've checked the PostgreSQL License,
and had a question.
http://opensource.org/licenses/PostgreSQL

It seems that the license requres a "LICENSE" file
in the target product
[quote]
> Then put the license into a file called "LICENSE" in
> your software distribution.

But I couldn't find "LICENSE" file in current PostgreSQL source tree,
instead found a "COPYRIGHT" file.

It seems the contents of the "COPYRIGTH" file are all required by the
license.
So I have confused why PostgreSQL has a "COPYRIGHT" file instead of
"LICENSE".
Anybody knows the reason?
And is this non problem thing?

regards,
-----------------
Tomonari Katsumata