After all, a lot of malware needs to be attuned to the hardware and OS. Malware that works on Windows does not work on Mac OS X or Linux, malware that infects Firefox will not infect Chrome or Internet Explorer. And the rise of "trusted sources" such as the iTunes Store and Amazon's Kindle store means that most readers won't encounter malware-infected books when they do show up.
That isn't to day that there won't be malware infections, but to stick to the infection metaphor, deadly epidemics are actually pretty rare. The diseases that stick with us are not the sort that kill off their hosts, and so I suspect that destructive malware will remain at the edge, as long as our "immune system" remains healthy.