Just a few comments(even if a little late):
1-) Please, Tom, before anything you need to stop using the "whining" term, as it was said before, it sound disrespectful and can push people away, as creator of the game you need to treat somethings with a more professional view than personal. People will always complain, you won't be able to satisfy all and taking it personally will injure your health and stress you out. Yes you are a player of the game. But he is also the boss. So for some things you need to be more professional(and this goes for all the staff and people that helps you, players or not, volunteers or not, the "Dev team" title, for example, represents you and BM official view of things) when it comes to this matters, free or not you still provide a service to a worldwide group of people. Not just your friends.
2-)Remove or in anyway discourage the OOC messages, removes the "playing with friends" aspect of the game. How can i become friend with a realm member if I can't send them OOC message? OOC message serves not only for venting and in-realm complaint, it helps people to know each other outside the character they created.
3-) I would suggest something more like, instead of adding a text asking if the message you're about to send should be OOC. Add it to the players page. There you can say:
If you have found a bug, please report it to the bugtracker (hyperlink).
If you want to complain about the game, please use the forums (hyperlink forum).-> Here can also be created a topic informing people of where to go (General talk go here, game function go here, magistrate case here, etc)