The guys at Blizzard Entertainment love their holidays, and Halloween is no exception. The town squares and inns throughout the World of Warcraft are decorated for the holiday.
As if mere decoration weren't enough fun, you can also go trick-or-treating at the inns. You can only try trick-or-treating the innkeeper once per hour, and sometimes you're the one who get's tricked. For instance, I once received candy, once received a wand that turns friends into ghosts, and once got turned into a toad (I got better!).
And at least one of the traditional Halloween party games has been implemented in the World of Warcraft: Bobbing for Apples!
The developers at Blizzard are obviously having entirely too much fun with this stuff.