yup, counties get a lot bigger on average the farther west you go. sparse populations and probably kind of a "frontier" mentailty when the counties were formed where people didn't care as much about access to government services, as opposed to some counties east of the Rockies that I know were split because the county seat was too far from a vocal segment of the population.
just for fun, AZ does have some dupes, just not in the list Chas made: Santa Cruz (CA), Yuma (CO), and Graham (KS, NC).