SkyVegas is regulated by Alderney and powered by Netent casino games. Both Alderney and Netent do not accept citizens from the United States of America.
I sent an email to the SkyVegas support to get a clear explanation. Here is their answer :
We do not have a license to operate in the US though if you are a resident in the UK you can bet with us.
As part of the US gambling law, SkyVegas preferred to step back from the US Markets. However, some online casinos still continue to accept US citizens. Check our top 3 US Casinos.
Technically, you could play to SkyVegas if you signed up from abroad. For instance if you are in vacation in Vietnam or in Mexico, you could play to SkyVegas while you drink your Mai Tai. However, you should not use a US address and an american credit card (from Wells Fargo for instance).
This is the same problem as "signing-up from abroad". You could use a VPN to play to SkyVegas, but you would need to have a real address outside of the US (with phone bill at your name for instance). If you have a sister abroad, for instance in the Brazil, it could work. Otherwise, in case you win a $9,000,000 jackpot, SkyVegas could block your funds..
We know that Bovada is currently accepting US citizens. It is powered by Top Game software and offers a nice welcome bonus.