Thats a very valid point. Hadoop does a lot more than handle the basic logic of MapReduce (which btw, is not terribly complicated). Fault tolerance, preemptive duplication of tasks in case of unexpected slowness, etc. are all part of the ugliness that Hadoop takes care of on large clusters.
That said, I can see this being useful for prototyping MapReduce code quickly in Python without going through the hassle of setting up Hadoop and coding in Java.