Blizzard always make sure they have as many domains registered as possible for their franchises and often pay out reasonable chunks of change to acquire them if they are already owned by someone else. Typically we have seen domains purchased by Blizzard for around $10,000 from other parties, which is a decent amount if you are sitting on a domain they are after.
Recently Blizzard acquired the domain WarcraftBattles.com and are also seeking to acquire HeroesofWarcraft.com. However, it appears the UK registered owner of the domain is not wanting to part with it and Blizzard has now filed a complaint with the National Arbitration Forum, the organisation who can decide if they have a legitimate right to the domain.
Blizzard already owns HeroesofWarcraft.co.uk which they registered back in September last year.
Nobody knows why Blizzard are pursuing the domain, are they working on a new Warcraft strategy title perhaps?