I'm not convinced that DBAs are needed at all.
As an application developer, I think that a DBA is unnecessary - any application-side modifications should be done by the application developers - a DBA neither could nor should make such changes (indeed, those changes should need to go through the same change control and QA as any other change from the development team, so the DBA would become one of the team).
Likewise, anything which is NOT a change in the application is a sysadmin issue and should be handled by the operations team with THEIR change control policy - again not DBA territory.
When I find out what one is good for, I'll let you know.
In my opinion, DBAs can't really do much performance work, because 99% of that is going to come from modifying the application, which operations should not be doing.