Yes, you are missing something. Data Guard is not simply a new marketing name for former Standby Database, it trully is a new concept. You are wrong in assuming that a standby database uses only archived redo logs as a mean of transporting changes from primary to the standby - with Data Guard there is a new concepts of Standby online redo logs, to which changes might be written simultaneously with those on primary side.

Depending on which Data Guard configuration you choose and on how much performance/availability impact you allow on the primary database, you can have your standby site not lagging as single transaction from your primary. This is called "no data divergence/no data loss".

And yes, Data Guard is trully a disaster recovery solution. In fact, appart for database replication it is *the only true disaster recovery* solution I can think of. RAC for example is certanly not.