The PSTN has nothing to do with modern broadband.
I'm finding some of the comments here discussing the POTS/PSTN network a little amusingly irrelevant and I think it's also something that clouds political and media discussion a lot. It's a bit like a discussion about steam trains. It's 1980s technology, used for legacy services and has no bearing on broadband speeds at all.
Modern broadband networks are using the same copper lines as PSTN services, but they've absolutely nothing, whatsoever, to do with TDM circuit switched technology behind traditional PSTN/ISDN services, they just share the copper wiring for the 'last mile'. Cabinet launched VDSL doesn't even use the full line back to the exchange. In fact it would be a lot easier to just provide the VDSL service without the dial tone and the long line.
The telcos all initially had a notion that POTS/PSTN was important enough to warrant rolling out MSANs to street cabinets and provide dial tones down the line and various vendors came up with solutions for this, However, with the death of demand for domestic / residential POTS services, the massive increase in use of mobile phones and a consumer acceptance that you can provide a phone service using VoIP from a local ATA in the router or a VoIP handset has changed all of that. There's been a major loss of interest in ripping out the old TDM equipment and replacing it with modern modern gear, rather they will run it down until it's got far fewer users left, then make a switch to much smaller scale equipment for the laggards who still need dial tones.
If a cable company can get away with providing POTS using VoIP from a device in your home, there's no reason BT, Eir, Deutsche Telekom or AT&T can't do exactly the same using VDSL or FTTH and a similar device.
Offices increasingly don't use ISDN or PSTN lines either. There's a very rapid move going on to smaller businesses using hosted PBX in the cloud type services and VoIP handsets - it allows home office workers, remote sites, hot desking and far fancier routing options than was ever possible with your own PBX. Meanwhile larger companies are increasingly using SIP trunks in place of ISDN to plug their PBX gear into the telcos.
Telephony is just an app on a data network. Nobody cares about POTS equipment anymore, least of all the vendors or the telcos. They just want to sweat the last bit of useful service out of existing gear before they have to rip it out.
What's holding things up in the UK at the moment is lack of real competition. You've multiple brands all using OpenReach networks and then you've got Virgin offering a fairly mediocre cable modem service. If you'd a real FTTH player in the market, or if Virgin really cranks up the speed, OpenReach will be forced to respond. Until then, they'll all keep charging you high prices for mediocrity.