It has more to do with the settlement patterns of the U.S. and the "frontier attitude" toward the West than anything else. The West was sparsely populated (still is, for the most part), and laws were a lot less restrictive, in general, than most of the "eastern" states. Also, there had long been a tradition of gambling in the mining and logging camps of the West, so gambling was indeed a part of the culture.
In a way, it is a little like comparing Australia to Europe; your culture developed in a more open and less restrictive tradition than the "old world".