There's Community Managers, Creative Developers, Developers and Designers, as well as Customer Support and official accounts. All the major accounts are there, and there's even the option to include @ tweets, so all the ones a given account sends to everyone. You can use the tool to read all the tweets from just one account, removing the need to click around to different accounts. And there's even a mouseover for every account, showing their Bio as a tooltip.
If you would rather see the accounts on your own terms, and follow all the Blizzard Twitter accounts, you can check out WoW Insider's guide to Blizzard Twitter accounts.