You don't understand the rule. If you catch in the air, but land on the ground and drop it, it's incomplete. THAT'S THE RULE. I'd study the rulebook, if I were you.
I think you need to reread the rules. On an interception the ground cannot cause a fumble nor a incomplete if the player intercepting catches it in the air.
I do believe there is a difference on this ruling between the pros and college. I believe Mike is right about the ground being a down in college, but I may be mistaken. I'm the wrong guy to officiate on this.
"You don't understand the rule. If you catch in the air, but land on the ground and drop it, it's incomplete. THAT'S THE RULE. I'd study the rulebook, if I were you."
The ground cannot cause a fumble. So said by the sportscasters here.