You're almost certainly right that it's an accommodation. The convolutions early Christian authorities went through to convert the English were quite remarkable.
"Do not destroy pagan temples, but convert them to Christian use so that the people will feel more comfortable coming there." "If the people insist on sacrificing an animal, let them do it – just so long as they sacrifice it to God."
Both of these instructions are to be found in a letter from Pope Gregory to Abbot Mellitus, who had come to England with St. Augustine. The letter's dated 601. It's quoted extensively in Bede's Historia Ecclesiastica.
York Minster is the only church in Christendom ever to have hung mistletoe within its walls - and the fact that it is York Minster means an archbishop must have made the decision.
What's remarkable about the two sites you mention is that they suggest (very strongly) that people were still worshipping in stone circles as late as the seventh century a.d. Interesting.