From what I know or what I perceived of the calls was this: (I'm not saying I'm right, just simply the way I saw things)
The Safety
My father and I looked at the rule and essentially as long as no one else had touched the ball and the returner remained within the end zone he should be able to pick up the ball outside of the end zone and bring it back in for a touch-back.
The Non-TD
In normal speed it was really hard to tell where his second foot touches, in slow motion its clear as day obviously, but also the ball isn't in the receivers possession completely, the ball was moving around a lot before and after he came down to the ground. This would explain why it was called an incomplete pass and because of this there wasn't a review because it wasn't a scoring play.
But this also strikes me with some inconsistency in the calls because the exact same thing happened with the Calvin Johnson catch that we challenged and they deemed it a catch, so why not this one? Or in the other case Megatron's catch should have been reversed.
Jordy's "muff"
He called the fair catch got the ball and was simply waiting, I believe the whistle was already blown as well, and in his waiting he was just toying with the ball. I guess think of it as after a catch or a run play the receiver or runner gets up to hand the ball to the ref but he ends up dropping the ball on the ground.
Inconsistencies
Erik Walden gets called for the arm to Stafford, the play was supposed to be dead but the two were still in play and Stafford threw the ball, Walden was trying to make a play on the ball didn't happen and came down, gets called for a very minor hit if you ask me (the nature of the hit and call was similar to that time Woodson got called for the "hit" on Eli). Now the same thing happens on the Green Bay side of it Matt Flynn is running and Vanden Bosch comes up behind him and as Flynn stops Vanden Bosch puts an arm on him, no call though. What I don't get is these things get called but when you knock down the QB after the ball is out it doesn't get called. Flynn gets pancaked when he makes the one TD to Nelson (off the false start), and that's fine but a simple arm to the chest after trying to bat the ball down should not be considered a penalty in my opinion.
"excessive celebration"
I really can't see how Grant's Snow Angel is any bigger of an "excessive celebration" than say the Lambeau Leap, "Discount Double check", or that stupid little dance Scheffler did. He was already on the ground, dude just ran about 40 yards for a TD he's tired you think he wants to get up right after that? Let him do his celebration on the ground if he was already there to begin with.
My thoughts on the Challenges thing.
I believe the reason they don't allow coaches to repeatedly Challenge if they win the call is because it would make the games last longer.