IMHO, one thing we can blame emphatically BT for is the inadequacies of their DLM algorithms.
On a long line, a 15dB SNR Margin, rather than 9dB (or even six) can easily reduce speed from over 3Mbps to less than 2Mbps. Of course, DLM is there to serve a purpose (providing stability) but, as has been well-documented in many threads, there's a lot of folks on 15dB DLM target margins for no good reason. Personally I'd like to think BT would be made to improve their DLM software, before we start digging up the roads all over again to overcome it's deficiencies.
Also, it's not just old copper that causes the problems. In Milton Keynes, I believe, the problem was that they wired the town with aluminium as it seemed like a good idea at the time (not that long ago).