Is this new or just not enforced? I know you have the exit row agreement pop on the web site so I find it odd.

From usair web site....

If your seat assignment is in an exit row, you must check in with an agent. You can use a kiosk as long as there is an agent there to print your boarding pass. If you’re seated in an exit row and traveling out of Phoenix, the kiosks near security check point A and B do not have agents near by and you should check in downstairs.