Don't worry, Jack - I think we both got the wrong end of each others point, and I certainly didn't intend to imply you're a fool.
ANYWAY, back to the actual point of the conversation...
I agree that the deep cleaning performance of a machine does depend on a number of factors, but IMO, the brushroll is one of the biggest of those. Even a carpet sweeper can remove surface dust and dirt and I think we would all agree that the machines known for their deep cleaning ability are the ones with thick, dense, relatively stiff bristles. The suction is obviously another factor, and I've said before, I have no issues with the suction power of Dyson cleaners, just the messy emptying, filter washing (both being unfortunately unavoidable) and brushroll (which is why I prefer Dyson's cylinder machines to the uprights).I would certainly like to see a brushroll more in the style of a Kirby, Oreck or Sebo brushroll as these have all proved for years that they do groom the carpet to a very high standard. The short, sparse bristles are not for me, I'm afraid.
Having said that, one does have to bear in mind the current market. In the UK, thick carpets are out and hard-wearing, low pile carpet and laminate floors are in, obviously eliminating the need for such a deep cleaning brushroll. On the other end of that scale, many people did buy very good quality deep pile carpets and have not replaced these (my Mum and several friends parents, for example, still have carpets fitted in the 70's and 80's). Perhaps Dyson could develop and market a specific machine specifically designed for homes with thicker carpet with a more dense brushroll? Sort of like the animal, all floors, allergy etc variations on the same model, a Dyson "deep clean" would certainly have a market I think.