As ragged has indicated, there are a number of digital only radio services, though the commercial and BBC local radio choices will depend on your location (as will quality of coverage - some people complain about being in a DAB black spot).
From the BBC, national stations include 1 Xtra, 6 Music and Radio 7 (initially called BBC 7 I think), plus Asian Network.
Where I live, here in North Wales, I have never heard signals on BBC World Service nor BBC Parliament, but 'local' stations (which I have heard, but are weak and depend on the aerial and other wiring causing signal changes) include R Merseyside (approx 30 miles), Manchester and Stoke (each approx 50 miles). On FM I can get R Stoke and R Shropshire, and R Wales (no sign of it on DAB).
Commercial stations include Jazz FM (which is no longer on FM from Manchester!) and a lot of others, some 'national' and some local from Liverpool or Manchester.
FM still has better audio quality for most (all?) stations, because at present most stations limit the sampling rate, so while they used to say DAB was CD quality they never claim that now. The problem is that for commercial reasons they have squashed a lot of stations onto each digital transmission (multiplex) and therefore cut down on quality, so now they market DAB as giving lots of choice and gloss over any sound quality issues. Even on BBC 'Feedback' when 'quality' is asked about, the head of radio talks only about poor signal strength and how the network of transmitters will fill in the gaps over the next few years (another 60 were on the books for 2010/2011 to offer greater coverage) but the audio issues are ignored at the moment, by the BBC (they are, however, launching an internet based higher quality service for Radio 3, presumably because while the audience may be small, they are a vociferous group with some strong personalities and mix in the right circles to cause trouble for the BBC!)
BBC Radio 3 was 256 kbps initially, but has been reduced to 192 kbps. Most stereo stations use 128 kbps, though even Radio 4 is sometimes cut from 128 kbps to 80 kbps so they can have sports coverage on Radio 5 Sports Extra, and they have been using that during the Cricket, or Formula 1, so they can still carry regular Radio 5 broadcasts and have continuous commentary without any news/ weather/ traffic breaks on this 'extra' service]. Radio 7, which has comedy, drama, and some programming for under 10s [best recorded, it runs 5am to 8am or thereabouts] is in MONO only, at 80 kbps...
By juggling with the sampling rates they can mix and match quality vs number of stations. If they had gone ahead and closed 6 Music and the Asian Network, they would have had a bit of spare data transfer rate available so could have made Radio 7 go up from 80 kbps mono to 128 kbps stereo (would make sense as they include brand new material commissioned for Radio 7, and some recent Radio 4 drama and comedy gets onto 7 as well). Radio 5 doesn't need stereo as it is a sport and news station, but I suppose some discussion shows, interviews and so on, could be enhanced if it had stereo sound.
Now compare those sampling rates with a CD which you can sample at 320 kbps to play in an MP3 player, and you can see that there is bound to be some quality loss. If you have ever heard sound slips at different sampling rates (eg using iPlayer for some live radio show, and then clicked on 'lower bandwidth') you may notice some 'dullness' in the sound, as some of the higher frequencies are not recreated in what you hear (just 'thrown away' during the sampling process).
Audio quality is currently not better on DAB (higher sampling rates are being used on satellite, and FM audio quality is also higher in most cases) but I would never say there's "no point", as the audio is generally acceptable and for Radio 5 a massive improvement over the AM (Medium Wave) broadcasts, unless you are close to one of the BBC transmitters!
It is also possible for stations to split their output, either to cover sport on one signal (eg DAB) and music / talk on their FM output. R Stoke has different programmes some evenings, DAB and medium wave carry one thing, while FM links up with R Shropshire and R Hereford + Worcester with a music programme.