Many big BIG international conventions take place in Vegas. If there's an industry for it, they probably have a convention in Vegas. It makes sense for Vegas the city to incentivise cheap flights/hotels, which makes it more appealing for business groups to meet there. And of course come spend money in the casinos and restaurants after a hard days work of conferencing! I know a few people that went to Vegas just to party for a long weekend etc. But the vast majority of people I know that went to Vegas, went "for work". Also yes, CES is a big deal.