Vegas casinos would need affiliates for the same reason other companies need them–competition. While Vegas could become a hot spot (in our theoretical world where owning an online gambling site is legal in the USA), the individual companies would be fighting for business as they do now.
They all advertise and that’s were affiliates come in.
I’ll be voting early again this year (a popular choice for Nevadans) and Berkley is getting my vote again. 