Here's another article along the same lines to ponder....
Water Changes in Reef Aquaria:
http://reefkeeping.com/issues/2005-10/rhf/index.php
For me, weekly water changes are more than just taking out old water and putting in some new. I clean the living heck out of the foams in my mechanical filters in the changewater, break down and clean all powerhead parts, and siphon the detritus from our three reefs' BBs.
I also keep a log of test results for alk, Ca and Mg. Ocassionally check for nitrate, but with lots of macroalgae in my systems, nitrate is usually 0 ppp. The log also contains records of what and how much alk, Ca and/or Mg a system gets according to the test results and the following reef chemistry calculator...
http://home.comcast.net/~jdieck1/chem_calc3.html
I have ocassionally gone more than a week without doing the above maintenance, and life in the tank suffers from additional algae on the glass from the detritus not exported from the systems. Additionally, powerheads do not pump the same capacity because the foams in the prefilters are clogged with detritus.
So, for our systems, a water change is much, much more than just swapping old water for new.