According to a Which survey reported in the press some weeks/months (doesn't time fly) ago Dyson are not only the most expensive vacs but also the most complained about. Whether people felt more obliged to complain when they went wrong because of the high cost of the purchase whilst those who bought cheaper machines simply binned them and bought another cheapo doesn't seem to have been explored.
On the subject of suction allied to colour of top perhaps LL could enlighten us. Is BM a purple or yellow top?