Years ago, I was told by a Dyson customer care representative, that the DC06 only lasted about 10 mins before needing the batteries recharged.
This might well be true: the DC06 apparently had a brushless switched-reluctance motor, no doubt an early version of the Digital Motor.
And if you take this train of thought further: remember the poor battery life of the later Dyson Cordless models. The DC06 motor would probably be even more power hungry at that time.
I was also told that a few wealthy Japanese businessmen might have bought the odd one.