That's also not completely acurate:

  postgres=> SELECT now(), now(), clock_timestamp(), clock_timestamp();
              now              |              now              |        clock_timestamp        |       clock_timestamp

-------------------------------+-------------------------------+-------------------------------+------------------------------

  2015-09-11 09:57:00.414422+00 | 2015-09-11 09:57:00.414422+00 | 2015-09-11 09:57:00.419087+00 | 2015-09-11 09:57:00.41909+00

Now() stays the same for the entire statement as well. clock_timestamp() doesn't.