The reason why some sites don't state that is because it should be common sense that as a USA resident you are not allowed to do any online gambling at all, whether its bitcoin or not.
You can use a VPN but keep in mind that if you send your withdraw to coinbase or xapo, they will blacklist your account because you are not allowed to send/receive transactions from any gambling btc addresses.
This is not true! Most US states allow online gambling, it is not allowed to send money to online gambling sites.
Despite of this, the operator has to state which countries are not allowed to use the service.
How does that make sense then? If you aren't allowed to send money to an online gambling site how are you suppose to gamble then? Kind of counterintiuitive.
From what Coinbase told me, it doesn't matter what state you are in, they will blacklist you if their software detects funds arriving or being sent to an online bitcoin casino.
yes,there are many accounts banned by Coinbase if they detect funds being sent to or from a gambling site,it is not for the US citizens only
many pinoys were complaining as they used one gambling site that didn't change the deposit address at all and probably withdrew from a set of wallets as well
most of the casinos,though,change their addies very often so it is hard to detect if the money is coming from a casino or not
of course it is not worth to risk and check,you will get banned and funds confiscated by Coinbase
the only advantage coinbase had was no fees,not sure how is it now since I have around 50k satoshi there left