While true that they can’t just allow whatever to be said in game, the player created content is not rated at all. Player created content (Names and chat) are not made ahead of time then reviewed and rated.
Blood and Gore, Crude Humor, Mild Language, Suggestive Themes, Use of Alcohol, Violence
- Online Interactions Not Rated by the ESRB
That goes for all Blizzard games and platforms. Instead of the game rating, Players have to follow the Code of Conduct for the company. The same policy applies to everything. All games, all chat, all names, etc.
The Code of Conduct is very family friendly - more so than the game ratings individually. Diablo games with an M rating still follow the same no profanity/masked profanity rules.
Yes, there are two different sets of rules. One for the game company, and one for the players. The rules for players are far more strict than what companies are held to.