My primary skepticism was because the news articles I read seemed to imply all of those things without actually giving much in the way of details. And they got a lot of the technical details wrong.

The thing that convinces me the most right now though, is the EPA FAQ page that Tom linked earlier. Until he linked it, I hadn't seen it. It specifically accuses the software of defeating the emissions tests (though it seems to stop just short of saying it was deliberate), and says that the vehicles on the road are emitting 40 times more pollution than the laws allow. Since the EPA has the most information about it, though not all of it is public, they are in a position to know the most about it right now, and therefore what they're saying carries weight, so I'm certainly on the side of believing it for now.

The poorly-researched and poorly-written news articles I saw sure made it look like a lot less than they were saying it was, though.