They do, but alot of times, they do so because their original story didn't happen exactly as they described it in the heat of the moment on a 911 call. I would say that in most of the cases like this that I've seen, the real story happens somewhere in the middle. I can say with confidence that if he hit his child, there would be some kind of bruise or mark, the girlfriend (based on everything I know of motherly instincts) would have been far too upset to later retract her story, and the police would have detained James for longer than they did and given a stiffer punishment than they did.
To me, the story seems like alot of flames being fanned by the media who sometimes can pitch a story in favor of the direction that gets the most attention and causes the most heads to turn.
I think that if this is the only thing that is holding the Bills back from drafting him, then they should think again.