A dilemma indeed. Having read the links it appears planning consent for a new mining project and supermarket were granted before Unesco threatened to withdraw WHS status and the threat is really the only power Unesco have in this scenario. I understand part of the requirements of having WHS status is that nothing is significantly changed (i.e. new building can only take place on an existing site of a redundant building) so Unesco have some justification. However, to block the new projects would mean loss of jobs and prosperity to the area so seems a bit unreasonable.

PS: You mentioned Stonehenge and Avebury WHS - I did hear there are plans to split this into two sites carrying World Heritage status whereas at present it is one site.