Meanwhile German customers have discovered Dyson devices and seem to love them so why should Dyson try and cut itself off from this market?
He isn't. Import duties aren't an impossible barrier, they're just a tilted playing field. I can buy plenty of non-EU made products quite easily for products whose makers have to pay duties intended to protect some inefficient EU industrial lobby. And so with Dyson - the markup on his cleaners is more than enough to support whatever WTO duties the EU have. JCB appear to have a similar view.
I've actually been doing the Brexit analysis for my company (in a wholly different field), and we've concluded that there's bugger all benefit to us or our UK customers from being part of the EU. Most of the business cry-babies over Brexit are corporate dullards who fear change, not the entrepreneurs or commercial people who are always looking for opportunity.