[jiggy2011]

There is possibly a problem with user education here.

Running software on your computer that is not set to automatically pull down and install security patches to me seems like a far bigger problem than not running AV software. Windows does warn you if you turn automatic updates off , but afaik there is rarely such a warning about third party software.

In your friends case it would seem that he is not getting updates from adobe, since viewing a PDF file should not cause third party code execution so he must be getting PDFs that are exploiting his PDF reader (presumably adobe fixes these quickly as they arise).