I mean, it could be user specified, but it is typically better to assume that a 'service' could have an issue on first attempt. There are a lot of reasons, legitimately that it would fail, including the service being unavailable, too many questions being asked by the user, etc. 5 is a pretty good default to let the backoff do it's job and wait for the service to become available again. 

Personally, I'm not a fan of 'magic numbers' either, but, something > 1 is really necessary to be fault tolerant...