for enabling exchanges for broadband, and it's the exchange that you are connected to that would need to be enabled.
I'm not sure why you are getting conflicting information - on the one hand you say that you've been told you live too far from the exchange, and yet you also say that BT have told you your exchange hasn't reached its 300 trigger point. From that I deduce that you would be too far from the exchange, even if it did reach the trigger point. Is that the situation?
I'm not sure about greed, but it obviously isn't viable for BT to enable every exchange in Britain, regardless of demand - at least not in the short to medium term. The people who live half a mile down the hill are presumably on a different exchange - one that has been enabled?