It is primarily the sports books which got the email to shut down, and not other gambling sites. And because of this I don't see US following the same steps, unless they want to go after every gambling site to shut them down.
It seems that it is not only restricted to an unlicensed sportsbook. FortuneJack has shut their doors to UK gamblers as well
We have added Great Britain into our list of blocked regions because online gambling is illegal there. In the past we had blocked several US states for the same reason. Although, we are working with gambling commission to resolve the issue as soon as possible and meet the country regulations.
For the bolded part, it seems like they are looking into purchasing a license there so that they could keep on providing their service for the UK gamblers or that it is an excuses from them. It will be just a matter of time I guess before the UK gambling commission hit another top gambling sites.
There isnt any other non sportsbook gambling sites that announce things about shutting their doors down for the UK gambler apart from FortuneJack so I suspect this could be a precautions moves from FortuneJack or either than they are based on UK