The key point here is that Clojure-style vectors have logarithmic random reads/writes, while Okasaki's aforementioned deques do the same in linear time. Clojure

The key point here is that Clojure-style vectors have logarithmic random reads/writes, while Okasaki's aforementioned deques do the same in linear time. Clojure uses the persistent vector by default, so it's essential that people can port their usual imperative vector algorithms and expect to get acceptable performance. Hence the focus on random access. As to amortization, operations on Clojure-style vectors have pretty much zero variance (modulo the size of the vector). There is no resizing, no reordering, no rotation or whatever, it's just the exact same algorithm every time.