date_trunc should be called date_round?

It's stated in the docs that date_trunc is "conceptually similar to the
trunc function for numbers.".

So, trunc(1.1) = 1, trunc(1.9) = 1, and so on.

But, date_trunc behaves like round function: round(1.9) = 2.

Example:

idel=# select date_trunc('milliseconds', '2009-01-01
12:15:00.000999+02'::timestamp with time zone);
date_trunc
----------------------------
2009-01-01 11:15:00.001+01
(1 row)

fidel=# select version();
version

----------------------------------------------------------------------------------------------------------
PostgreSQL 8.3.7 on x86_64-unknown-linux-gnu, compiled by GCC
gcc-4.3.real (Ubuntu 4.3.3-5ubuntu4) 4.3.3
(1 row)

Or am I again completely misreading something?

Mike