twiggy, assuming edam means Witch, it's usually Bosch or someone. They don't generally test any machine with larger than normal capacity, Dyson would have been included because it only has a larger than normal capacity, if it had a smaller version they would have included that instead.
Part of Witch's criteria these days is reliability, and Dyson's is crap overall so even if performance is good - as in Vacs - they don't get recommended because they break down a lot.
If she means GH then their standards are different anyway.
Have just checked - Witch's last best buys were 2 Bosches, 1 Siemens and 1 Tricity Bendix - 5.5kg usual capacity, and you have to remember that you need to halve that for non-cottons (eg duvets) because they take up up more space for the same weight. If you must wash a duvet in a normal washer add a couple of towels. (Bashes it about a bit.)