You'll notice that in my original post I said "not even getting into positive and negative punishment", also I suggested that reputation decay was an example of negative reinforcement, not punishment.If the aversive stimulus (reputation decay) is stopped by logging in and grinding rep, then one does so more frequently in order to prevent reputation decay.
It's not a punishment, because reputation decay happens even if you do nothing.
You'd hardly classify it as a reward though would you? You've failed to note that the aversive stimulus can be also be avoided, and with greater rewards, by playing a different game that doesn't offer punishment for failure to grind. Not a good choice on FD's part because it polarises players into the two extremes of " hardcore" (who avoid decay by playing) and "disinterested" (who avoid the negative reinforcement by going elsewhere).
There's more than one way to Skinner a cat.