the original article regarding the drop in casualties came out.
The truce began in February 2005. Since then, there has indeed been a drop in attacks. However, there has been a
drop in Israeli casualties starting with Defensive Shield in March 2002, whih increased after the beginning of the construction of the barrier in 2003. In addition, the
location of attacks shifted; most of them tended to be where the barier wasn't complete.
IOW, in 2004 you have a drop due to the barrier; in 2005, you have a
further drop due to the truce. To put in another way, the drop in 2004 is due to the barrier; the drop in 2005 is barrier+truce, but the barrier wasn't mentioned in the article because it's not a new factor (the Shabak didn't state that the barrier was
ineffective). If the barrier was not effective, the level of casualties from April 2002 till February 2005 should have remained roughly constant rather than dropping significantly.
I should note that Avi Dichter (head of the Shabak until 2005) credited the barrier with stopping quite a few terrorist attacks, including a planned attack on a school in Yoqneam.