I had a male dog, that was never around other male dogs. He was not fixed. He lifted his leg to go after he matured. I disagree with the whole see other male dogs do it theory. He was semi dominant.
I currently have a male mastiff mix that was fixed at 18 months when he was turned into rescue.. so it was late, He is 3 yrs now, and generally will squat to go, but will lift his leg on occassion. He also has not been around other males to see them go. He is semi dominant.
Could it be because of the confidence level of the dog? Thats my theory. Dog's that have low confidence, don't like getting up on things, which require their feet off the ground. We used to use climbing on things, and walking on unsteady things, to build confidence in dogs. Some temperment tests for dogs involve odd surfaces as part of the test (ATTS) When I had puppies, we had their play yard full of "unsteady" things they could walk and climb on.