Thanks for the link. The document defines fraud as "the basic conditions for receipt of benefit, or the rate of benefit in payment, are not being met".
Let's say that the conditions in this case are that you present a signed-off claim form from your doctor.
So, wicked Fred decides he's "got some back pain" because his mates told him that he could claim DLA that way. He goes to the doctor, makes a big fuss and the doctor signs off his claim.
When he then makes his claim to the government, he presents his duly-signed-off form. He's met the conditions for the benefit, so technically this isn't fraud, even though you and I would clearly see it as such.
Maybe I'm completely mistaken, but it seems strange that a benefit that seems so easy to claim fraudulently is subject to such a low fraud level.