Strange error message when reference non-existent column foo."count"

I encountered this today and it was quite surprising:

select version();
version

------------------------------------------------------------------------------------------------------
PostgreSQL 9.3.5 on x86_64-unknown-linux-gnu, compiled by gcc (Ubuntu
4.8.2-19ubuntu1) 4.8.2, 64-bit

create table foo as (select generate_series(1,3));

As expected, the following fails:

select count from foo;
ERROR: column "count" does not exist
LINE 1: select count from foo;
^
But if I change the syntax to something I thought was equivalent:

select foo."count" from foo;
count
-------
3
(1 row)

It works! This was quite surprising to me. Is this expected behavior, that
you can call an aggregate function without any parentheses (I can't find
any other syntax that works for count() sans parentheses, and this behavior
doesn't occur for any other aggregate)?