Bittrex is a crypto only exchange, no fiat.
The only place that regulates pure crypto exchanges is Washington State, and both Bitfinex and Poloniex don't service customers from there as part of the terms and condition.
Their legal teams may have determined that revoking service from Washington customers is sufficient, but at least in the case of Polo, their own terms of service contradict their legal compliance requirements:
Poloniex is registered with the Financial Crimes Enforcement Network (FinCEN) as a Money Services Business (MSB), registration number 31000091844018. Poloniex may be required to file details of Account activity to FinCEN from time to time. Poloniex may also be required to provide information to government agencies as required by law to other state or federal agencies.
They openly admit that they are an MSB, yet they do not hold any licenses anywhere. It's almost like they announced to FINCEN, "Hey, look! I'm an unlicensed MSB, operating in 49 US states. Come shut me down and fine me!"
Personally, I get the risks, and they
can be worth it. But you need to be a good trader capitalizing on the massive volatility, and you need to minimize the time you hold funds on these unlicensed exchanges,
especially after what happened to BTC-e last month. Don't expose too much of your funds to this risk, and mitigate it as much as possible.
And if you're a losing trader, don't bother. Get your funds out.