Sure, it sucks for the people of Detroit who, frankly, have needed a win worse than Cowboys tackle Alex Barron needs anonymity, but the refs got the ruling correct. Furthermore, this is a rule that - despite what many are saying - should not be changed in the offseason.
I know, I know. How can this be?! Clearly Johnson had the ball. Blah Blah. Just hear me out...
The entire purpose of this rule is to provide the clear, undeniable ability of a referee to determine the catch was made. Decisively. Conclusively. With a rule that dictates a receiver must control the ball through the process of the catch, there should be no doubt of if a player made the catch or not. I don't know if Johnson would have held on or not, but I know that the ground contacted the ball after the catch, and the ball came free, and the Johnson got up to celebrate. Perhaps it was a bit of salesmanship on his part, going immediately into the celebration because he knew that the ground was the primarily catalyst for the ball leaving his palm.
If Johnson had simply held onto the ball, it's an easy touchdown. He either A. felt the need to get up and celebrate early before ensuring he controlled the ball, or B. knew the ball was coming loose and tried to "sell" the play to the best of his abilities.
The NFL has these rules to ensure conclusiveness on these calls. It's the reason that the "force out" rule no longer applies and a receive MUST land both feet in bounds. It's to take away from the judgement of a referee that a receive "would have landed in bounds if" the defensive back hadn't pushed him out. That word "if" is the big problem. By taking out that "if" and making everything cut-and-dried, there is less controversy over these calls.
It's like baseball. A player is either safe or out. There is no tie (except for an All-Star Game Bud Selig would like to forget). It's either a catch or incomplete.
The purpose of the rule is to remove the gray area. It's black or white. Either or, but not both. And in Week 1, the Lions couldn't catch a break. Well, they could have, had they possessed it throughout the catch. Instead, their attempt to start the season 1-0 fell incomplete.