First, I have to say that's a BEAUTIFUL Hoover! I had a Rainbow D which served me very well for 15 years. I don't mean to discredit your observation at all but, I suspect that as a whole, those of us here probably vacuum more frequently and more thoroughly than the average populace. Chances are that dirt never lingers long enough on our carpets to get ground in very deeply no matter what machine we're using!
When I bought this house two years ago there were a couple rooms with wall to wall carpet. I'm not sure if the previous residents even owned a vacuum, and if they did they certainly didn't use it very often, or it was a really POOR performer. I got tired of my Electrolux Diamond Jubilee wanting a new bag every five minutes, and even my Kirby Heritage II went through several bags in the first couple months while I was busy painting and doing other things prior to moving in. I couldn't believe how much dirt I kept pulling up. When I finally removed the carpet there was, I kid you not, at least a 1/4 inch layer of fine gritty soil covering the padding under the carpet. YUCK!