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

select version();

                                               version                                                

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 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:

But if I change the syntax to something I thought was equivalent:

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)?