Jeremy is bang on with his answer - I have no idea on the legal situation but it is 100% sponsorship and attendance support - Just look at the Bahamas last year where CAP SpringBreak really struggled to find sponsors for the event or CAC in Canada which barely got 70 people to attend and neither of those were even in the US.
I think it also isn't just operators, there are many affiliates that are not comfortable attending an event such as that on US soil - They quite rightly feel they are literally placing themselves in full view of the authorities.
I really hope a US event isn't far off as I would love to smash it up in Vegas again on an expense account

- The first event back there is going to be huge! Hopefully within the next 2 years we will be back at least with poker......