First of all I don't wish to discredit your knowledge on these things as you obviously know more about some of the more intricate things then I do
Lets look at it like this. DSL has two factors involed in you getting the speed. Line length and contention of pipe from DSLAM to ISP.
Cable has the single factor of contention from customer to CMTS. I would like to think core is a situation that doesn't require as much thought as the access networks, after all 'Plusnet issues' don't appear to be apparent on ntl.
So yes, a telephone loop is not shared like cable and cable does not have the same contention point. However channel bonding can negate the smaller share, even though its a wonder now to those who cannot monitor a uBR of its usage, how a DOCSIS 1.1 64QAM system can hold the the allocate users on a card and still can see 10mbit, so I cannot see why the same cannot be said when the speeds are higher offered on a system which has greater aggregate bandwidth with somewhat the same ratio. Not to mention the evil traffic shaping gear they have too
BT's 21 CN network of bringing fibre closer to the home, well ntl is already there with fibre to the node. So if we are going to compare upgrades, BT are moving fibre up to negate the effects of line length and try and offer better speeds come ADSL2+, VDSL2 or whatever else there is by then, as opposed to ntl who are making use of the existing bandwidth that is already there. In fact, even before channel bonding, I know ntl are using a second downstream in one area that isn't Guildford.
It cannot be denied that the gigabits of bandwidth available on coax networks is there, its just not being used, whether that be due to finance, technology, needed technology upgrades or dumbass management. I'm guessing possibly all four with ntl
