AFAIK the accounts are not controlled centrally. How it works is that the project owners set up a site/webapp, which has javascript that interacts with wallet extensions installed on the user's browser. Members of the DAO uses the site to do various actions, for instance buying tokens or making votes. The site sends the request to the wallet extension to be signed, and then it gets broadcasted to the ethereum network. At the end of the day, the wallets are still controlled by the user, it's just that hijacking the site allows them to fool a massive number of users that don't pay close attention.