Not that there is anything at all positive about this war, nor would I suggest that these individuals aren't leaving because of it, but it is always good to consider all sides of any discussion. From the same BBC news article:

Former defence junior minister Don Touhig disputed the findings, arguing that the evidence was purely anecdotal. "We've had lots of assertions of large numbers of people leaving the forces or going absent because of Iraq. In 2001 2.65% of the forces went absent... in 2005 it's 2.63%," he said.