FM was invented in the 30s as an improvement on AM radio. AM is still around and has uses but its use is limited and its not as good quality as FM. FMs problem is that it got a limited spectrum and cannot handle many stations. There can be lots of interference.
There was a working group in the UK which recommended a move to Digital but the timescale has not been set and is much longer than what has happened in Norway. According to the FT article the UK Switzerland and Denmark are watching to see how the transition in Norway goes I assume to inform how to plan a transition in the UK.
It's on the way out its just a matter of when! :)
We still have some AM stations that are mostly news and sport I think. Music obviously benefited from the move to FM. We have loads of stations on DAB, but I'd argue that quality is more important than quantity. I know they just want to sell the bandwidth, but many will not get many listeners. I'm not rushing to get a digital radio in the car as I mostly listen to podcasts these days