This sort of "not my problem, guv" disclaimer culture is becoming more common. On the face of it, it may seem reasonable. How can anyone guarantee there's nothing malicious on their media? Sure, they may follow best practice and scan with mutliple products, but there's always a chance something will slip through.
That of course is true, but it doesn't follow (at least in my mind) that you then wash your hands of all responsibility. Certainly in the commercial world we can't. Not only are companies, not unreasonably, expected to take proper precautions but in many cases are held contractually liable for the impact of any viruses they supply, unwittingly, with their deliveries. In many cases there are specific clauses to this effect in terms and conditions.
Antivirus vendors would be committing commercial suicide if they started putting such disclaimers on their products. If they're prepared to accept responsibility for their media, why can't the Government? If you ship something to a customer, you have to take the can if it's got problems, even if they're not entirely your fault. Buck-passing is not something that, in my experience, endears you to your customers.
So remember, next time you pick up a laptop or USB stick left on the train by some hapless civil servant, make sure you virus scan it carefully (of course I'm joking, if you genuinely do find something, take it straight to the local Police, not Fleet Street).