Ok I thought I would post an idea I have had for a while, its about why they decided to change Ben's history for the film. My thought that it wasn't simply that they thought theirs was more interesting that than the 616 and UFF but that the change was need to fit a "Vision" they had for the film, a vision that in some way all four characters in some way wanted the powers they get and that Ben's background had to be changed to fit that.
Johnny
I'll start with Johnny since he is where my theory is thinnest, mostly because we don't really know how they plan to show him. But I suspect that he is not all that happy at "Baxter", that he is there mostly because his Dad wants him there. He would probably prefer to be a pilot or astronaut or something like that, something with speed and excitement. His street racing is something his family doesn't approve of but its his way of rebelling. So when the powers hit he gets speed and flight and that sort of cool stuff.
Sue
For Sue I suspect they will have it that she feels like she is a bit of a second class member of the family due to being adopted, that she tends to be overlooked. She probably doesn't go on the mission due to being overlooked, the reason she gets the powers is that she is stuck in the lab alone due to being overlooked. You get the idea. So when the powers his the girl who feels invisible gets the ability to actually be invisible.
Reed
For Reed I think the reason for those powers is something we have seen lots of times in the trailers and tv spots, Doom's "death". When Doom falls we see Reed trying to save him, reaching out to grab him but not being able to reach far enough. So when the powers hit he is thinking about that and so ends up with the ability to reach further.
Ben
Now we reach Ben, if you look at the normal history for Ben there is no way he would want to be turned into the Thing. 616 and even UFF Ben are tall, handsome, strong, tough, successful guys, Ben even protects Reed from bullies without the need for any powers. But when you switch Ben to being a short guy that got bullied by his brothers it fits better. Becoming the Thing makes him tough, strong, someone who can protect others from being bullied. For UFF and 616 the change was completly unwanted but with the film version there is a bit of wish fulfillment.
Its just a theory but its the sort of thing I could see the film makers finding cool, that on some level they all wanted the "disabilities" they were given, and that Ben had to be changed to make that fit.