For anyone who wants to argue that this is a PHP-caused anomaly, note also http://www.securityspace.com/s_survey/data/man.200501/apachemods.html
-10% followed by +11% the following month:
http://www.securityspace.com/s_survey/data/man.200502/apachemods.html
Big swings like that are almost always artificial. One or two big domain parkers switching versions or toggling the server header. You can't deduce much from that.
-Rasmus
