I doubt you mean anything very judgmental by 'normal', but this still jumped out at me. In Ruby an index-based for loop is pretty unusual. The for loop is non-idiomatic, and it also has a scope leak: https://gist.github.com/3232118.
Anyhow, no offense taken at all. But I would be shocked if any Rubyist did use for.
As far as creating a new array (or several new arrays) goes, there are some new considerations such as composability that are starting to be valued more highly than efficiency. And pure functions are more composable than ones that mutate the existing data.
Granted, the n < 0 case could still be handled in a way that's more efficient but still pure by allocating an array and filling it backward rather than using two reverses and an iterator.