It's like I've said before, Jon, Dyson's success lies purely in clever marketing and not in actual product. Dyson created a problem for people that next existed.
Generally speaking, most bagged vacuums do not lose enough suction to reduce performance so dramatically that the machine doesn't pick up. The machine will still pick up the same amount with a full bag as it does with an empty one.
And lets face it, who REALLY gave a flying fig about emptying a vacuum bag? We just got on with it. Bag, bin, done. Infact, disposable paper bags were added to vacuums to make them easier to empty. Prior to this, all vacuums had cloth shake out bags. And then we took the bags away again? Bit of a step back.
But Dyson's "Say goodbye to the bag" campaign tapped into a gap in the market. It planted a teeny tiny seed of doubt in consumers minds, that grew and grew into something so big that the market was completely taken by storm. DC01's were flying off the shelves, but they really weren't all that good. The suction is poor, the build quality isn't great, the brushroll is pathetic. There were other, cheaper, higher performing and better made machines available at the time from Hoover, Electrolux, Panasonic and Hitachi, but still the lowest performing and most expensive cleaner was the one that was selling. All due to marketing.
In credit to Mr. D, his very clever campaign worked. He's a very intellegent man and knows what he's doing. But sadly, his understanding of promotion hasn't meant his vacuums are actually any good.