Dockerfiles are just "run anywhere", not "run any time". Maybe I should have made it clear. The creator still needs to maintain his Dockerfile. Maybe http://blog.docker.io/2013/11/introducing-trusted-builds/ will make things easier.
I think the level of detail you have worked fine for the writing style, my comment is somewhat nitpicky. Your statement is generally true, if they use the dockerfile they posted then it's extremely likely to work for you too.
It was mostly a clarification for people reading that the dockerfile doesn't guarantee repeatable builds.
