Iowa has come a long way, but we're not perfect. We don't really need the permit, but if we don't have one we have to wait a week to take it home, as opposed to same-day-bring-home with the permit. My LGS, however, requires the purchase permit to make his job a little easier. Not like he does much anyway, but the point is there.
But really, the purchase permit, or, "Permit to Acquire Pistols and Revolvers," is just that; for pistols and revolvers. Long guns do not apply to this permit. A CCW permit will also fill in for a purchase permit in my neck of the woods, though I'm sure it's the same way all across Iowa.