This is actually a bit weird.
The only games that get their own official domains are full titles, not expansions. TBC, WOTLK, Cata and Mists haven't had any official .com domain before.
Yes, they've (almost) all had domains.
theburningcrusade.com and mistsofpandaria.com were both poached by the same Korean company the day they lapsed from Blizzard's ownership.
wrathofthelichking.com is still owned by Blizzard and, as of a couple days ago, linked to the battle.net site
cataclysm.com has been owned by another company since 1998 - so Blizzard could never have picked it up.
Looking for Raid: you will never find a more wretched hive of scum and villainy. Come - we must be cautious.