My black Rucarta Rancher actually IS a tiny bit thicker than the (larger) Cowboy model with the same handle material. Measured at the pivot end with a dial caliper, the Rancher is 0.52" thick, the Cowboy is 0.50". Just a subtle difference in finishing, I'm sure. But, it's all the more noticable on the smaller knife. I like that 'beefy' heft, though.
Coincidentally, just for comparison, my stainless Case Sodbuster Jr. is exactly the same thickness as the Rancher (0.52"), measured at the pivot end. My large stainless Case soddie is 0.56" thick at the pivot.