Vegas? because...
The reality is that Vegas has an almighty shedload of available rooms, at reasonable cost (cheap rooms == more disposable dollars to lose at the tables...), cheap airfare to/from for the same reason, any amount of entertainment options (including the naughtier places off-Strip), and within driving distance to the southern California population centers, leading to it being a VERY popular locale for conferences.
Biting the hand that feeds IT
