Why can't the student take the Amer Opport Credit on his return when pg 20 of Pub 970 says he can if the parents don't claim him (even if they qualify to claim him)?

The table in the upper left corner of pg 20 of Pub 970 indicates that the dependent can claim the American Opportunity Credit if they aren't claimed as a dependent by their parents (even if their parents were entitled to claim them as a dependent), yet the software won't allow the credit to be taken on the student's own return unless he says he can't be claimed by someone else.