Ian,
The Sebo BS36 & BS46 were designed as commercial equipment and over the years have proved to be extremely rugged and reliable. I have examples that are over 20 years old that still perform as new. The Dyson was, in a recent survey, voted the least reliable domestic vacuum cleaner, whereas the sebo domestic model was voted top.
The single motor of the Dyson must provide both airflow and brush power whereas the Sebo has two motors.
Aside from the above, the other factor is that when a professional cleaner comes to clean a carpet, Mrs Housewife expects to see professional equipment, and this is not the same when she is thinking "I've got one of those in the cupboard" (maybe even a later model).
