It's one thing for Henri to rock up a few miles down the road with an unprepared car. It's another to jet across the ocean. So I can understand why Dyson aren't up for it. There's not really any basis for comparison between the two.
Certainly wouldn't make a trip to the US to see Dyson.
Does sound like there will be a couple more American entries according to John Dagys, one being a first-time entrant.