Unfortunately that's not entirely accurate. If the salting algorithm is known, or can be deduced from a few accounts with known passwords, then it becomes relatively easy to determine which accounts are using common passwords. You wouldn't be able to brute-force a specific account using this technique. But if you suspect that a lot of users have the password "zergling" then you can quickly calculate the hashes for that and compare them to the hashes in the database. That'll gain you access to several accounts.
The moral of the story is that you still need a strong password even if you know it's going to be hashed.