Radio - I don't have any hard facts, but I'd expect that a very large portion of total radio listening occurs in situations where it could not be received via the NBN. In the car where it's mobile, at work where the boss is OK with it as long as there's no cost to the company and so on.
Cars aren't going to be wired to the NBN that's for sure, and I doubt that too many bosses would be willing to pay the cost of having a radio running at work. In any event, if someone is listening via that means then they no longer have any reason to listen to their local station, or indeed any conventional station with advertising. The radio stations would be well aware of this and so aren't likely to go down the NBN track ever.
As for TV, I can see that it may happen but it will be content, not picture quality, that drives it.
People didn't go to digital TV because there's a better picture. They went digital in order to get extra stations, hence Tasmania had the highest takeup rate for many years since it was the only state with a digital-only mainstream channel.
Likewise it was similar with other things like CD taking over from records and tapes - it wasn't the audio quality but rather the convenience that pushed the change. And then when MP3 largely replaced CD, well that's a decrease in quality but convenience and price has driven the change.
I've had a HDTV at home for over 5 years now. But if I turn it on right now, the vast majority of broadcasts are not in HD because the networks haven't really adopted it on a major scale. Sure there's some, but it's nowhere near to being universally accepted.
TV via the NBN is quite likely a goer, but I'd expect the actual picture to be 1080 at best and possibly less. It's content that will drive it, not a minor improvement in picture quality.