There wasn't conclusive visual evidence on video to change the call. It could be argued Shipley was losing control of the ball while he was going down, but then he regained control before hitting the ground. That's what it looked like to me. Once he hit the ground he lost control again, but his knee was already down and the ground can't cause a fumble.
I have to say, I was sweating out that very thing. Chris and Kirk did not seem to think it was an issue, but if it had been called a fumble -- point taken about the refs' odd perspective all night -- it would have been hard to overturn.