I'm not speaking for Marco, but another issue with dollars is tax accounts (and especially VAT accounts) for British companies have to be in pounds, so there's overhead in doing the conversions, tracking the exchange losses/gains, etc. We also have to reverse charge the VAT on those transactions as well (though I'd be surprised if the majority of business owners know they have to do that).

About 90% of my company's expenses are in dollars, so I've had to become proficient at dealing with it, but I imagine it's more annoying for companies who only make the occasional USD transaction, especially as they may have smalltime accountants unfamiliar with or unwilling to deal with the exchange rate stuff properly.