It seems the trademark was "Published for opposition in early 2007, February 13th to be exact.
This means that any competition to the name Diablo now has a chance to oppose the trademark for whatever reason.
WOW was released a year after the name was published for opposition, but that doesn't seem to be the case for Diablo 3.
If there is no successful opposition it will become an official registered trademark and finally ready to be put for sale.
For a refresher, this trademark includes rights for a movie title: "ENTERTAINMENT IN THE NATURE OF AN ONGOING TELEVISION PROGRAM IN THE FIELD OF CHARACTERS AND PLOTS BASED ON A VIDEO GAME; AND PRODUCTION AND DISTRIBUTION OF MOTION PICTURES"; BUT it doesn't look like it will be titled "DIABLO II: SALVATION" as that trademark is now DEAD.
Read: DEAD, like Starcraft: Ghost! LOL (yes, that is officially dead Abandonment Date December 4, 2005)
I would also like to confirm Blizzard's plans on producing in-game communication software. Perhaps you head of this, but Battlechat - "Virtual network telecommunications services, namely, providing an interface for the electronic transmission of messages and data including voice, text, and message transmission" was filed at the USPTO on January 11, 2008