I would try to log into your account because when I do that, I get the same thing. However, the upgrade option on my account says differently:
As a valued AT&T customer, this line qualifies for discounted equipment pricing when you sign a new 2-year commitment.
We can offer you an additional discount up to $50.00 off regular 2-year commitment pricing and a waived upgrade fee on most devices. Additional discounts do not apply to iPhone.
iPhone Upgrade
As a valued AT&T customer, we can offer you a discounted iPhone upgrade with a new 2-year commitment and an $18 upgrade fee.