Both are done for efficiency, it requires to copy the environment variables for each request, so we want to keep number of environment variables as small as possible.
For the default stdout, maybe it is not necessary, we receive some requests to redirect it. If we can do it once during initialization, will avoid doing it for each request.
Both are minor details, so there should not be a problem do it one way or the other.
We also thinking to redirect rails exceptions from our stderr.log to the application log, but have no clue how to do it.