Ian,
I think your correct, I could do a great job with a tooth brush and a spray bottle......but it might take me a while to complete that livingroom!! I do most up scale homes, and market by asking for referrals from my own customer base. Many of these homes are very lightly soiled, and really no need to have a power house. If I was doing more commercial or rental units, I would most likely use a different system.
The US has seen a huge shift to the big high heat direct drives, that darwf machines made just 5 years ago. They are very high heat, and often the techs complain of burns, from contacting the brass. I can see the value of these High Vaccuum (very fast drying) and High Heat (just desolve it all..very fast) but I worry about safety in peoples homes.....lets say one of those line were to spilt?? (I'm very safey oriented...to a fault!)
My main focus is leather repair, and I just use carpet cleaning to get my foot in the door to sell other services, stake my claim in that household. Jon
P.S. Ian, I love your website!! I have been looking around this site at all the well crafted websites, most everyone looks like they have invested in high quality websites.