Arthas got a statue and it is not even Warcraft's Anniversary. If the surprise is the Diablo's statue really feels like Blizzard found out about the anniversary yesterday and then said "Oh... Anniversary... Right, I ... knew it. Here, take ... this ... chocolate! I bought it this morning to celebrate! Hurray!"
While I do agree that we haven't got much information for some time on the development changes around runes (that is, IMHO, the main reason for the delay) and this is a good sign of the release date, the point that if it was a release date then it would be incredibly powerful to announce it at the 15th anniversary it just too compelling.
You can always think that they may have not done it due to the holidays, so it wouldn't have the staff ready to make the official announcement, but I think this is not so important.
It may be some lore info, action figures, new business models or something like that. Maybe even a movie.