Re: Simples Really.
The problem is BT really don't mind that scenario. If they could get rid of you they would, because they see no profit in you, well certainly none in terms of giving you a free infrastructure upgrade, that's been made very clear.
They really wish they didn't have a legacy rural customer base, at times.
Pricing it that way, just gives BT an excuse to do even less for you. It's also not fair because the cost of providing Broadband to the exchange/cabinet is exactly the same (equvalent of providing a local water pump, in days gone by).
The fact the signal deteriorate in quality over copper between you and the cab, is well your problem, and why Openreach needs to be completely separate from BT.